DK2848180T3

DK2848180T3 - Dishwasher with the cooled vessel wall

Info

Publication number: DK2848180T3
Application number: DK14001765.8T
Authority: DK
Inventors: Albert Johann Loichinger; Ingo Gau; Ernst Dober; Stefan Flück; Dustin Becker; Marcel Quadrelli; Beat Wellig
Original assignee: V Zug Ag
Priority date: 2014-05-20
Filing date: 2014-05-20
Publication date: 2016-08-22
Also published as: EP2848180B1; EP2848180A1; PL2848180T3; SI2848180T1

Description

Technical Field

The invention relates to a dish washer with a vat for receiving dishes, with a cooling device for cooling at least a wall of the vat and with a controller for controlling the cleaning process. The invention also relates to a method for operating such a dish washer.

Background Art

In dish washers of this type, the cleaning process comprises a classical cleaning phase, in which the dishes are cleaned in one or (normally) several cleaning cycles with process water, partially by supplying cleaning agents. Furthermore, the cleaning process comprises a drying phase, in which the dishes are dried.

The controller heats the vat and particularly the dishes to be cleaned arranged therein before the drying phase, normally by heating the process water up to a relatively high temperature of e.g. 50 - 60°C during the rinsing process. Thereafter, the drying phase starts, during which a cooling device, e.g. in form of a fan, is activated in order to cool at least a wall of the vat or an exchange surface by the vat air. In this way a drying effect occurs as the hot process air initially absorbs moisture from the dishes in the vat and then arrives at the cooled wall by convection or diffusion, where it releases the moisture. WO 2010/142569 describes a dish washer with a warm water intake and a cold water intake and with a program step for cleaning the dishes to be cleaned and with a drying step. WO 2006/069834 describes a dish washer with a heat exchanger at least at one side wall of the cleaning chamber with a condensation surface for drying moist air in a treatment room. DE 3941226 describes a dish washer with a refrigerant channel, which is arranged at the walls of the cleaning tank and serves for the optimization of the drying of the dishes to be cleaned.

Disclosure of the Invention

An objective of the present invention is to provide a dish washer and a method of the type mentioned at the beginning with an improved drying efficiency.

This object is solved by the subject of the independent claims.

Accordingly, the controller of the dish washer is adapted to regulate the cooling device during the drying phase such that the center temperature of the vat lies between 1° and 10°C above the temperature of the cooled wall. "Center temperature" of the vat is understood as the temperature of the process air in the center of the vat.

The basis for this invention is that fog is produced in the area of the cooled wall, i.e. the air condenses spontaneously in suspended droplets, during at least a part of the drying process in conventional methods. This fog production is a less efficient drying process as compared to the direct condensation at the wall of the vat, along which the water can drain. Furthermore, the fog can remoisten the dishes and hence counteract the drying process. Furthermore, condensed droplets substantially constrain the exchanging process caused by diffusion or convection. It shows that the fog production can at least be avoided to a larger extent if the temperature difference between the middle of the vat and the wall is limited to around 10°C. However, the temperature difference should be at least 1°, because the drying rate decreases otherwise.

It has been noticed that particularly good drying results are reached if the temperature difference is between 2 and 6°C.

Because the temperature usually decreases during the drying phase, the controller is adapted to increase the cooler power of the cooling device in several steps or continuously during the drying phase in order to maintain the desired temperature difference.

The length of the drying phase is at least 10 minutes, particularly at least 20 minutes. The drying phase is understood to be the time period, in which the cooler power increases in several steps or continuously and the temperature of the wall lies below the center temperature by the mentioned difference.

In an advantageous embodiment, the cooling device has a control loop for regulating the temperature of the wall to a set value. This control loop can at least partially be implemented in the software of the controller. Furthermore, the controller is adapted to decrease the set value in several steps or continuously during the drying phase. In this way, it can be well guaranteed that the temperature difference remains in the desired range independently of the efficiency of the cooling device (which e.g. can be dependent on the ambient temperature).

The invention is particularly suited for dish washers in which no means are provided for actively circulating air inside the vat. Actively circulating is understood to be a circulation by mechanical means, like e.g. fans or blowers, in contrast to a passive circulation due to convection effects. The problem of the fog production is particularly well-known in devices in which the air is passively circulated and therefore the transport of moisture in the air is based on free convection and diffusion.

The invention also relates to a method for operating a dish washer with a vat for receiving dishes and with a cooling device for cooling at least a wall of the vat. In the context of this method, a cleaning process comprising a cleaning phase and a drying phase is performed, wherein the wall of the vat is cooled by the cooling device during the drying phase. Thereby, the cooing device is controlled during the drying phase such that the center temperature of the vat lies between 1° and 10°, in particular 2° - 6°C, above the temperature of the wall.

Brief Description of the Drawings

Further embodiments, advantages and applications of the invention result from the dependent claims and from the now following description by means of the figures. It is shown in:

Fig. 1 a schematic section through a dish washer,

Fig. 2 the course of the temperatures and of the cooler power and

Fig. 3 a Mollier diagram of air loaded with water.

Modes for Carrying Out the Invention

Device configuration:

The dish washer according to Fig. 1 has a vat 1 for receiving the dishes to be cleaned. Dish racks, sprinkler arms and other means for receiving and for cleaning the dishes are provided inside the vat 1 in a known way. These components are not of center importance in the present context and are therefore not shown in the figure .

On the front side the vat 1 is closed by a door 2. Furthermore, the device has a cooling device 3 for cooling at least a wall of the vat 1, in the present example for cooling the back wall 4 arranged opposite of the door 2. In the present example the cooling device is formed as a fan which sucks in ambient air from the socket area of the front side of the device. The air circulated in this way sweeps along the back wall 4 and is blown out again through the front side of the device above the vat. Therefore, the fan is adapted to cool the wall 4 by ambient air.

Furthermore, a controller 5 is provided, which controls the operation of the components of the device according to user inputs. The controller 5 is a process controller which is adapted to operate the presently described process steps.

Furthermore, the device has (not shown in Fig. 1) a water circulating system, as known, comprising a fresh water supply for supplying fresh water, a water circulation system for circulating water from the sump of the vat into the sprinkler devices, as well as a system for discharging used water into the sewer system. Heating means are arranged at the water circulation system and/or at the vat for heating the process water. A detergent supply allows the controlled, process controlled supply of detergents like e.g. cleaning liquid or rinse agent. Furthermore, in the embodiment according to Fig. 1 two (optional) temperature sensors are shown. A wall temperature sensor 6 serves for measuring the temperature of the back wall 4. A control temperature sensor 7 is arranged at a distance from the wall 4, preferably at a distance of at least 10 cm, and also measures the temperature at or inside the vat 1. The tasks of these sensors are described in more detail further below.

Operation:

In operation, the controller 5 controls the components of the device according to the cleaning program selected by the user. At least one of the selectable cleaning programs is adapted for carrying out a cleaning process according to the procedure described in the following .

In a first phase of the cleaning process, which is called cleaning phase here, the controller 5 supplies process water to the vat 1 for cleaning the dishes. This phase can comprise several process water cycles, e.g. a precleaning cycle without dishwashing detergents and a main cleaning cycle with supply of dishwashing detergent. Further process water cycles with or without supply of dishwashing detergent can be provided. The process water can optionally be heated in some of the process water cycles, typically to temperatures between 40 and 50°C. The process water is partially or completely discharged and substituted by new water between the process water cycles.

Preferably, the cooling device 3 remains switched off during the cleaning phase.

The end of the cleaning phase consists of a rinsing process, in which fresh process water and rinse aid are supplied to the vat 1. The water is heated to a relatively high temperature of about 50 - 60°C in order to supply heat to the vat 1 and particularly to the dishes. Then, the water is discharged.

Now, the cooling device is activated at a time tO. For this, it is referred to Fig. 2, which shows the course of the center temperature (continuous line) and of the wall temperature (dotted line) in the top diagram, and the cooler power (i.e. the electric power supplied to the cooling device) in the bottom diagram.

Initially, the cooling device 3 can (optionally) be operated with relatively high cooler power in order to decrease the temperature of the wall 4 rapidly about 1 - 10°C below the center temperature. Then, the cooling device is operated during the drying phase from time tl such that the wall temperature is set in the range of 1 - 10°C below the center temperature. Because the center temperature continuously decreases in the vat during the drying phase, the cooling of the wall 4 has to be increasingly stronger, as shown in the bottom diagram of Fig. 2, in order to maintain the desired temperature difference . A continuous increase of the cooler power is shown in Fig. 2 from time tl on. However, this increase can take place in several discontinuous steps. "Cooler power" is understood to be the power averaged over a time range of few minutes, particularly of maximum 5 minutes, which is supplied to the cooling device 3. In other words, the cooling can also take place e.g. in form of short "cooling impulses" of e.g. some seconds, wherein the intensity or the length of the cooling impulses is increased over time.

Furthermore, it is conceivable that the cooler power deviates from the described increasing course, particularly at the beginning (as shown in Fig. 2) or towards the end. The drying phase according to the claims is understood to be the time range identified in Fig. 2 between tl and t2, during which the cooler power increases in several steps or continuously and the temperature of the wall lies below the center temperature by the mentioned difference. The length of this drying phase is at least 10 minutes, particularly at least 20 minutes.

In the course of the drying phase, the cooler power is preferably increased by at least 50% in order to take into account the cooling of the vat temperature.

The effect of the drying phase can be shown by the Mollier diagram of Fig. 3, in which the amount of water per amount of air is plotted along the horizontal axis and the enthalpy along the vertical axis, wherein the latter approximately corresponds to the temperature of the air. The curve "cp = 100%" shows the positions with a relative air humidity of 100%. All points above this curve correspond to states with a relative air humidity smaller than 100%. All points below this curve correspond to non-stable, undercooled states, in which the water in the air starts condensing (fog production), wherein the tendency to produce fog increases with an increasing distance from the curve "cp = 100%".

If the temperature difference between the center temperature of the vat and the wall temperature is very high, the air will reach a relative humidity of 100% relatively early while approaching the wall 4, caused by the convection movement, which can lead to fog production at a significant distance from the wall 4. The fog droplets produced in this way usually don't reach the wall 4, but are circulated by the air flow to the hotter areas of the vat, where they evaporate again or condense at the dishes to be cleaned such that the drying looses efficiency .

In contrast to this if the temperature difference between the center temperature of the vat and the wall temperature is small, then a condensation occurs only shortly before or at the wall 4, and the chance is high that possible water droplets condensed in the air hit the wall due to its movement. In this way, most condensed moisture condenses at the wall and can discharge from there into the sump of the device such that it can be eliminated. Therefore, the drying effect is higher.

Remarks :

From the physical perspective, the invention is based on the idea that the air is not too much supersaturated at the cooled wall 4. This means, expressed numerically, that the parameter cp, which corresponds to the relation between the partial pressure of water steam in gas and the steam pressure at a given temperature, preferably lies between 1.04 and 1.05, which (depending on the absolute temperature and as outlined above) can be expressed as a certain temperature difference between wall and center temperature.

Preferably, as shown in fig. 1, a wall temperature sensor 6 is provided, by means of which the tern- perature of the wall 4 can be regulated. Hereby, the cooling device 3, the controller 5 and the temperature sensor 6 form a control loop, by means of which the temperature of the wall 4 can be regulated to a set value. The controller 5 is adapted to decrease this set value continuously or in several steps during the drying phase. The set value is preferably reduced by at least 10°C, particularly at least 20°C, during the drying phase in order to take into account the corresponding decrease of the center temperature, which is also at least 10°C, particularly at least 20°C.

Furthermore, as mentioned, a control temperature sensor 7 can be provided, by means of which the temperature at or in the vat 1 can be measured at a distance from the cooled wall. The signal of such a sensor is a measure for the center temperature of the vat 1, such that it can be taken into account for a better control of the cooling device 3. The lower the temperature at the control temperature sensor 7 is, the higher the cooler power has to be chosen. Particularly, the controller 5 is adapted to regulate the cooler power depending on the difference of the temperatures at the wall 4 and at the control temperature sensor 7 - the smaller this temperature difference is, the higher to cooler power has to be.

However, one can do without the control temperature sensor 7 in a particularly simple embodiment.

The set temperature for the wall 4 is reduced in this case during the drying phase according to a setpoint course determined by the device manufacturer. This set-point course is determined e.g. in experiments by the manufacturer such that the desired temperature difference is met for usual loads and process parameters.

Basically, one can do without the wall temperature sensor 6 in an even simpler embodiment. In this case the cooler power is increased stepwise or continuously during the drying phase according to a setpoint course determined by the device manufacturer. This set- point course is also determined e.g. in experiments by the manufacturer, such that the desired temperature difference is met for usual loads and process parameters.

In the embodiment shown so far, a fan is shown as a cooling device 3, which cools the wall 4 by means of ambient air. Alternatively or additionaly to this, the cooling device can have at least one of the following components: - A water tank can be provided for cooling, which is in thermal contact with the wall 4. Fresh water can be supplied into the water tank via a valve in order to cool the wall. - At least one Peltier element can be used for cooling, which is in thermal contact with the wall. - A heat pump can be provided for cooling, the evaporator of which is in thermal contact with the wall.

In the embodiment according to Fig. 1, the back wall of the vat 1 is cooled. However, it is also possible that another wall, e.g. one of the side walls, is cooled or that several walls are cooled.

Thanks to the here described embodiment of the device, the drying time and/or the temperature of the rinsing process can be reduced as compared to conventional devices, with the same drying result.

While preferred embodiments of the invention have been described in this application, it is clearly noted that the invention is not restricted to them and may be carried out in other ways within the scope of the now following claims.

Claims

A dishwasher having a tub (1) for receiving service, with a cooling device (3) for cooling at least one wall (4) of the tub (1) and with a control unit (5) for controlling a cleaning process comprising a a cleaning phase and a drying phase, wherein the control unit (5) is designed to heat the vessel (1) for drying the service and during the drying phase to cool the wall (4) of the vessel (1) with the cooling device (3), characterized in that the control unit (5) is designed to control the cooling device (3) during the drying phase such that a center temperature of the vessel (1) is between 1 ° and 10 ° C, especially 2 ° - 6 ° C, above a temperature of the wall (4), wherein the control unit (5) is designed to increase a cooling effect of the cooling device (3) during the drying phase in several steps or continuously, the length of the drying phase being at least 10 minutes, especially at least 20 minutes, whereby the drying phase is to be understood as the period in which the cooling effect increases in several steps or continuously, and the wall temperature is below the center temperature with said difference.

A dishwasher according to claim 1, wherein the cooling device (3) comprises a fan designed to cool the wall (4) from the outside by means of ambient air.

A dishwasher according to one of the preceding claims, wherein the cooling device (3) comprises a water container in thermal contact with the wall (4) and a valve for introducing fresh water into the water container, and / or wherein the cooling device (3) comprises a heat pump or a Peltier element.

Dishwasher according to one of the preceding claims, wherein the dishwasher comprises a control circuit (3, 5, 6) for controlling the temperature of the wall (4) to a setting value, and wherein the control unit (5) is designed to lower the set value in the drying phase for several years. step or continuous, especially at least 10 ° C, preferably at least 20 ° C.

A dishwasher according to one of the preceding claims, further comprising a control temperature sensor (7) with which a temperature can be measured on or in the vessel (1) at a distance from the cooled wall (4), wherein the control unit (5) is designed to control the cooling device (3) depending on a signal from the control temperature sensor (7).

A dishwasher according to claim 5, wherein the control unit (5) is designed to control the cooling device (3) depending on a difference between the temperatures on the wall (4) and at the control temperature sensor (7).

Dishwasher according to one of the preceding claims, wherein no means for actively circulating air in the tub (1) is provided.

Dishwasher according to one of the preceding claims, wherein the control unit (5) is designed to increase the cooling power by at least 50% in the drying phase.

A method of operating a dishwasher with a vessel (1) for receiving service and with a cooling device (3) for cooling at least one wall (4) of the vessel (1), wherein a cleaning process comprising a cleaning phase and a drying phase is carried out where the vessel (1) is heated to dry the service and where the wall (4) of the vessel (1) in the drying phase is cooled by the cooling device (3), characterized in that the cooling device (3) is controlled in the drying phase in such a manner. a center temperature of the vessel (1) is between 1 ° and 10 °, especially 2 ° - 6 ° C, above a temperature of the wall (4), where a cooling effect of the cooling device (3) is increased during the drying phase in several steps or continuously; wherein a length of the drying phase is at least 10 minutes, especially 20 minutes, where the drying phase is to be understood as the period in which the cooling effect increases in several steps or continuously and the temperature of the wall is below the center temperature with said difference.

The method according to claim 9, wherein the temperature of the wall (4) is adjusted to a setting value which is lowered in the drying phase by several steps or continuously, especially by at least 10 ° C, preferably by at least 20 ° C.

A method according to any one of claims 9 to 10, wherein the center temperature is continuously lowered, especially at least 10 ° C, preferably at least 20 ° C.