DE102010028726A1 - Heat accumulator for use in heat generation unit of e.g. baking oven, has housing for accommodating heat accumulator material, where heat conductivity of portion of housing is adjusted by applying preset electric voltage - Google Patents

Abstract

The heat accumulator (1) has a housing (10) for accommodating a heat accumulator material (2), where heat conductivity of a portion of the housing is adjusted by applying electric voltage that is less than 12 Volts. The material is a mixture of graphite and aluminum, and the housing has a thermally insulated layer (3) and a planar region (5) surrounded by the material, where the thermally insulated layer is made of Teflon(RTM: PTFE), perlite and/or ceramic fiber. The housing has an external layer (7) made of copper and/or aluminum. Independent claims are also included for the following: (1) a household heat treatment apparatus comprising a heat accumulator (2) a method for operating a household heat treatment apparatus.

Description

The invention relates to a heat accumulator for a household heat treatment device, a heat generating unit, a household heat treatment device with at least one heat accumulator and a method for operating a household heat treatment device.

DE 19824172 A1 relates to a cooking appliance with an energy storage and energy extraction system, wherein the cooking appliance with a cooking chamber, a heater, a circulation system, a steam generator and a measuring and control system, connected to the heating, the circulation system and the steam generator, and an energy storage and energy extraction system, connected to the measuring and control system. It can be provided that the energy storage and energy extraction system comprises an energy storage, which via a heater, preferably in Garphasen that require little or no energy, and / or Garpausen, and / or waste heat, such as heat from exhaust air and / or excess Steam, with energy is rechargeable. The energy store may comprise a material that is suitable for heat storage and / or consumes or releases latent heat during a phase transformation. The material may comprise a metal, a salt, a polymer, water, steam and / or superheated steam. The energy storage of the energy storage and energy extraction system can be arranged in an insulating skin of the cooking appliance. The energy storage and energy extraction system energy can be removed by throttling existing steam, adding water and / or evaporation of water on hot walls, in particular for vaporizing water and / or for heating a cooking process. The energy storage can be removed via at least one heat transfer surface energy.

It is the object of the present invention to at least mitigate the disadvantages of the prior art and in particular to provide a particularly compact possibility for controlled heat dissipation in a domestic heat treatment device.

This object is achieved according to the features of the independent claims. Preferred embodiments are in particular the dependent claims.

The object is achieved by a heat accumulator for a household heat treatment apparatus, wherein the heat accumulator has a heat storage material accommodated in a housing and a heat conductivity of at least a part of the housing is adjustable. Such a heat accumulator has the advantage that it can dispense with the control of heat emission to comparatively complex heat exchanger or other external heat release means. As a result, this heat storage can be made very compact, simple, error-prone and inexpensive.

An optional heat output from and into the heat accumulator can thus be controlled by adjusting the thermal conductivity of the corresponding part of the housing. The thermal conductivity may be continuously adjustable, in particular in a range of thermal conductivity between a lowest thermal conductivity and a highest thermal conductivity. A low thermal conductivity may in particular correspond to a practically heat-insulating state for the application, and a high thermal conductivity may in particular correspond to a state which is practically heat-conductive for the application. The housing can thus be at least partially switched between a "heat-conducting" or thermally permeable state and a "heat-insulating" state. The portion of the housing whose thermal conductivity is adjustable may serve as or provide a heat transfer surface or as a heat transfer area.

It is an embodiment that the thermal conductivity is adjustable by applying an electrical voltage. Such an adjustment or control of the thermal conductivity can be particularly easy to implement in terms of production technology and operation.

It is a development that the thermal conductivity is adjustable by means of applying an electrical DC voltage. This is particularly easy to provide. It is a further development that the thermal conductivity can be adjusted by applying an electrical alternating voltage. Also, a combination of a DC voltage and an AC voltage can be applied.

It is still an embodiment that the electrical voltage is not more than about 24 V, in particular not more than about 12 V is. This tension may be sufficient to adjust the heat-conducting state and at the same time is not dangerous to a human being. So can be dispensed with a complex electrical insulation.

It is a related to the application of an electrical AC voltage development that the AC voltage has a frequency between about 25 Hz and 150 Hz, in particular between about 50 Hz and about 100 Hz. Thus, an effective adjustment of the thermal conductivity can be achieved become. Also, such a network frequency can be used.

It is still a development that a value or degree of thermal conductivity by means of a variation of the applied electrical voltage (at DC voltage) and / or by means of a variation of the applied frequency (at AC voltage) is changeable. As a result, the heat emission and the heat absorption can be set very precisely. Thus, a lower voltage and / or a lower frequency may result in lower thermal conductivity.

It is yet another embodiment that the heat storage material comprises a mixture of graphite and aluminum. Such a mixture can store and release heat quickly, has a high heat capacity and is non-toxic, which is particularly advantageous in the event of damage to the housing. However, the heat storage material is not limited thereto, but may, for example, copper, if necessary, instead of aluminum, dispense with graphite, have a phase change material or include other suitable substances and combinations of substances, both liquid and solid materials.

In particular, a heat storage material made of a mixture of graphite and a highly conductive metal such as aluminum or copper can be produced in a particularly simple manner and in almost any desired form by a powder metallurgical process.

It is also an embodiment that the housing has at least one layer with an adjustable thermal conductivity, wherein the at least one layer at least partially surrounds the heat storage material.

It is still an embodiment that the at least one layer with the adjustable thermal conductivity has at least one electrode, for. B. with at least one comb or finger-like electrode area.

It is a development that the voltage is applied to a plurality of electrodes, which are separated by the material with the adjustable thermal conductivity. For example, the voltage may be applied to two electrodes disposed on opposite sides of the adjustable thermal conductivity layer.

It is a development that the voltage is applied on the one hand at least one electrode and another to an outer electrically conductive layer of the housing, wherein the at least one electrode and the outer layer are separated by the material with the adjustable thermal conductivity. The outer electrically conductive layer may for example be configured as described below, for. B. with aluminum and / or copper. In this case, the electrode can also be arranged on an outer surface of the at least one layer facing the heat storage material, for. B. by means of an additional electrically insulating, but thermally substantially permeable layer separated. In particular, in this case, the (eg only one) electrode may be formed lattice-shaped and z. B. substantially over the surface of the part of the housing whose thermal conductivity is adjustable extend.

It is yet another embodiment that at least one layer with the adjustable thermal conductivity Teflon, perlite and / or ceramic fiber. However, any other material is suitable which is heat-insulating in a non-stressed state and significantly thermally conductive under an applied voltage.

It is a further embodiment that the layer with the adjustable thermal conductivity has at least two layers of Teflon, pearlite and / or ceramic fiber, between which the at least one electrode is embedded. Such a situation can be easily produced and vary in thickness. In addition, a current flow through the layer in terms of its shape and a maximum allowable strength is easily designed in the production of the situation.

Preferably, each of the layers has a layer thickness of about 0.5 mm to about 1.5 mm, in particular of about 1 mm. This is a good compromise, in particular for Teflon, between a sufficient heat insulation in the heat-insulating state and a good heat-permeability in the heat-conducting state.

It is yet another embodiment that the heat storage material is enclosed at the part of the housing whose thermal conductivity is not adjustable by a thermally insulating material in a voltage-free state, which has the property locally by applying a voltage in a thermally conductive state. Thereby, the part of the housing whose thermal conductivity is to be adjustable can be easily generated by introducing at least one electrode into the heat-insulating material at this part. This facilitates production considerably.

It is also an embodiment that the housing has an outer layer of a good heat-conducting material, in particular copper and / or aluminum. The outer layer at least surrounds the layer with the adjustable thermal conductivity and ensures effective heat connection of the heat accumulator.

The object is also achieved by a heat generating unit, comprising at least one heat generating element, for. As a resistance heating element or a radiant heater, wherein the heat generating unit has at least one heat storage according to one of the preceding claims. Thus, a simple to produce and compact heat generating unit can be obtained, which is capable of both heat generation as well as heat storage, both functionalities are selectively adjustable and can also be operated in a mutual functional relationship to each other.

The object is also achieved by a household heat treatment device, wherein the household heat treatment device has at least one heat storage as described above or at least one heat generating unit as described above and at least one control unit, wherein the at least one heat storage or the at least one heat generating unit for adjusting its or its thermal conductivity is functionally connected to the control unit. As a result, the household heat treatment device can be made compact and can be operated effectively in terms of heat requirement or heat consumption.

The household heat treatment apparatus can be used, in particular, as an electrically operated cooking appliance (cooking utensils, oven, etc.), dishwasher (dishwasher, etc.), laundry treating appliance (washing machine, clothes dryer, etc.), small electric appliance (coffee machine, toaster, etc.) and the like. v. m. be designed. The household heat treatment device may also include an electrically operated cookware; the heat storage can then z. B. be accommodated between an attachment surface of the cookware and a bottom of the Gargutaufnahme. The household heat treatment device may also be provided for water treatment, in particular water heating and / or hot water storage, in addition, such. As a boiler, a heater or a part of it or a kettle. Thus, the heat storage can also be part of a hot water solar system. The electrical voltage for adjusting the thermal conductivity of the part of the housing of the heat accumulator can then originate in particular from at least one solar cell. For example, the at least one solar cell can be electrically connected to at least one electrode of the heat accumulator and thus serve as a voltage source.

• – in einem ersten Programmabschnitt das mindestens ein Wärmeerzeugungselement zu aktivieren und die Wärmeleitfähigkeit des Teils des Gehäuses, dessen Wärmeleitfähigkeit einstellbar ist, auf einen vergleichsweise hohen Wert einzustellen, insbesondere durch Anlegen einer elektrischen Spannung;
• – in einem zweiten Programmabschnitt das mindestens eine Wärmeerzeugungselement zu aktivieren und die Wärmeleitfähigkeit des Teils des Gehäuses, dessen Wärmeleitfähigkeit einstellbar ist, auf einen vergleichsweise niedrigen Wert einzustellen; und
• – in einem dritten Programmabschnitt das mindestens eine Wärmeerzeugungselement zu deaktivieren und die Wärmeleitfähigkeit des Teils des Gehäuses, dessen Wärmeleitfähigkeit einstellbar ist, auf einen vergleichsweise hohen Wert einzustellen, insbesondere durch Anlegen einer elektrischen Spannung.

It is a further development that the control unit has a program control which is set up for this purpose:

• To activate the at least one heat-generating element in a first program section and to set the thermal conductivity of the part of the housing whose thermal conductivity is adjustable to a comparatively high value, in particular by applying an electrical voltage;
• In a second program section, activate the at least one heat-generating element and set the thermal conductivity of the part of the housing whose thermal conductivity is adjustable to a comparatively low value; and
• - Disable in a third program section, the at least one heat generating element and adjust the thermal conductivity of the part of the housing whose heat conductivity is adjustable to a relatively high value, in particular by applying an electrical voltage.

By in the first program section high thermal conductivity of the part of the housing whose thermal conductivity is adjustable, heat generated by the at least one heat generating element can be transferred to the heat storage material in the heat storage element. In the first program section, the at least one heat-generating element thus heats both the household heat treatment device and the heat storage material. For example, in a domestic heat treatment appliance designed as an oven, the first program section may be within a preheating step or may correspond to the preheating step.

Due to the low thermal conductivity of the part of the housing whose thermal conductivity is adjustable in the second program section, the heat storage material is thermally insulated in the heat storage element. In the second program section, the at least one heat-generating element thus essentially heats only the household heat treatment device. For example, in a household heat treatment appliance designed as an oven, the second program section may correspond to a first part of a cooking step or cooking section.

By in the third program section high thermal conductivity of the part of the housing whose thermal conductivity is adjustable, stored in the heat storage material heat can be delivered and the household heat treatment device, even when the at least one heat generating element is turned off. Thus, in the third program section externally supplied energy, for. As electricity can be saved. For example, in a household appliance designed as an oven Heat treatment device, the third program section correspond to a second or last part of a Garschritts or Garabschnitts.

It is still a further development that a quantity of heat required for carrying out the third program section substantially corresponds to a heat quantity which can be maximally delivered by the at least one heat store. Thus, in a designed as oven household heat treatment device for a particular cooking program, the duration of the third program section, z. B. from empirical studies or calculations, from that amount of heat can be determined, which can be discharged from the heat storage for continuing or ending the cooking section. So the heat storage can be used very effectively.

• – in einem ersten Programmabschnitt das mindestens eine Wärmeerzeugungselement aktiviert wird und die Wärmeleitfähigkeit des Teils des Gehäuses, dessen Wärmeleitfähigkeit einstellbar ist, auf einen vergleichsweise niedrigen Wert eingestellt wird, insbesondere durch ein Anlegen einer elektrischen Spannung;
• – in einem zweiten Programmabschnitt das mindestens eine Wärmeerzeugungselement aktiviert wird und die Wärmeleitfähigkeit des Teils des Gehäuses, dessen Wärmeleitfähigkeit einstellbar ist, auf einen vergleichsweise hohen Wert eingestellt wird (z. B. indem keine elektrischen Spannung an das Gehäuse angelegt wird); und
• – in einem dritten Programmabschnitt das mindestens eine Wärmeerzeugungselement deaktiviert wird und die Wärmeleitfähigkeit des Teils des Gehäuses, dessen Wärmeleitfähigkeit einstellbar ist, auf einen vergleichsweise niedrigen Wert eingestellt wird, insbesondere durch Anlegen einer elektrischen Spannung.

The object is also achieved by a method for operating a household heat treatment device, wherein the household heat treatment device has at least one heat storage and at least one heat generating element having a heat storage material housed in a housing, wherein a thermal conductivity of at least a portion of the housing is adjustable, and in which

• - In a first program section, the at least one heat generating element is activated and the thermal conductivity of the part of the housing whose thermal conductivity is adjustable, is set to a comparatively low value, in particular by applying an electrical voltage;
• In a second program section, the at least one heat-generating element is activated and the thermal conductivity of the part of the housing whose thermal conductivity is adjustable is adjusted to a comparatively high value (eg by no electrical voltage being applied to the housing); and
• - In a third program section, the at least one heat generating element is deactivated and the thermal conductivity of the part of the housing whose heat conductivity is adjustable, is set to a comparatively low value, in particular by applying an electrical voltage.

In the following figures, the invention will be described schematically with reference to exemplary embodiments. In this case, the same or equivalent elements may be provided with the same reference numerals for clarity.

1 shows a sectional view in side view of a heat storage;

2 shows a sectional view in side view of a heat generating unit with a heat storage;

3 shows a sectional view in front view of an oven with a heat storage; and

4 shows an activation diagram of the oven 3 ,

1 shows a sectional view in side view of a heat storage 1 , The heat storage 1 has a heat storage material 2 with a mixture of graphite and aluminum. The heat storage material 2 is of a thermally insulating Teflon layer 3 surrounded on all sides. The Teflon layer 3 consists of two superposed, each 1 mm thick layers. On one side is in the Teflon layer 3 at least one electrode 4 introduced, whereby there a flat area 5 arises, the thermal conductivity is adjustable by applying an electrical voltage. The rest of the area 6 the teflon layer 3 remains permanently heat-insulating.

The Teflon layer 3 is in turn from an outer layer 7 surrounded by a good heat conducting material, such as copper or aluminum, the outer layer 7 from a receiving part 8th and one the receiving part 8th closing lid 9 consists. The lid 9 lies on the area 5 on. The Teflon layer 3 and the outer layer 7 together form a housing 10 for the heat storage material 2 , where the area 5 and the lid 9 then as the part 11 of the housing 10 can be considered, the thermal conductivity is adjustable.

By applying the electrical voltage, for. B. between 12 V and 24 V, to the at least one electrode 4 on the one hand and the lid 9 on the other hand (alternatively: between two spaced electrodes 4 ) can the area 5 be set to good heat conduction, so that the part 11 of the housing 10 can serve as a heat transfer area, which provides a good thermal connection between the heat storage material 2 and the environment of the part 11 of the housing 10 manufactures. Will no electrical voltage to the at least one electrode 4 Created, behaves the area 5 like the area 6 the teflon layer 3 heat insulating. Thus, by simply applying an electrical voltage, depending on the direction of a temperature gradient between the heat storage material 2 and the environment, a heat absorption or heat dissipation of the heat storage 1 be set. In this case, the thermal conductivity can be adjusted in particular continuously as a function of the electrical voltage. There is no further heat exchanger o. Ä. Required

2 shows a sectional view in side view of a heat generating unit 20 with a heat storage 21 , The heat storage 21 is basically the same as the heat storage 1 but have the lid 29 and the area below 25 the heat-insulating layer 3 whose thermal conductivity is adjustable, at least one return or a depression 32 for embedding a heat-generating element 33 on, which is designed here as an electrically operable meander-shaped resistance heater. Between the lid 29 and the heat generating element 33 is an electrically insulating, but practically thermally non-insulating layer 34 brought in.

This heat generating unit 20 has the advantage that it offers both a heating function and a heat storage function. Both functions can be activated simply by applying a respective electrical voltage. The heat generation unit 20 is very compact and simple. The heat generation unit 20 can also be assembled as a standalone unit and later installed in a household heat treatment device, which can further simplify manufacturing and logistics.

3 shows a sectional view in front view of an oven 40 , The oven has a cooking space 52 on, on the upper oven wall 55 a top heat radiator 53 and at the bottom of a lower heat radiator 54 is arranged. In the area of the upper oven wall 55 , which of the upper heat radiator 53 is covered, there is a first heat storage, for. B. the heat storage 1 out 1 , In an area of a lower oven wall 56 , which of the lower heat radiator 54 is covered, there is a second heat storage, z. B. the heat storage 1 out 1 , The heat storage 1 are aligned so that their lid 9 or parts 11 in the direction of the cooking chamber 52 demonstrate. Consequently, the heat storage material 2 over the part 11 of the respective housing 10 , whose thermal conductivity is adjustable, with the upper heat radiator 53 or the bottom heat radiator 54 as well as with the cooking space 52 optionally thermally coupled or thermally insulated.

The lid 9 can be directly to the cooking chamber 52 borders, z. B. by a recess in the respective oven wall 55 respectively. 56 , or through the respective oven wall 55 respectively. 56 be covered.

To control the heat storage 1 indicates the oven 40 a control unit 57 , which with the electrodes of the heat storage 1 is functionally connected and capable of applying a voltage to the electrodes for locally changing the thermal conductivity of the respective part 11 the heat storage 1 to apply. The control unit 57 may cause the application of the voltage, for example due to program control.

4 shows an exemplary activation diagram of the oven 40 , z. B. as part of a cooking program or controlled cooking cycle, as a plot of a cooking chamber temperature Tg against time (dotted line), a power supply to radiators 53 and 54 of the oven 40 (dashed line) and to the heat storage 1 of the oven 40 applied voltage (solid line), each in arbitrary units.

Through the cooking program, the oven should 40 are first heated to a predetermined cooking temperature Tg between a start time t0 and a time ta starting from the room temperature Tr ("heating section"). These are the top heat radiator 53 and / or the bottom heat radiator 54 energized, in particular continuously or clocked energized with a high duty cycle. For the thermal 'charging' of an associated heat accumulator 1 is simultaneously in a first program step P1 between t0 and ta during the heating to a heat storage 1 , which is an energized top heat radiator 53 and / or bottom heaters 54 is assigned, an electrical voltage applied. This can be in the associated heat storage 1 Heat to be stored.

The heating section is followed by a cooking section starting at ta, in which food to be cooked inserted into the oven is heat-treated, in particular cooked, at a substantially constant temperature Tg. During a first part of the cooking section between ta and tb, the top heat radiator becomes 53 and / or the bottom heat radiator 54 continue to be energized, z. B. clock-shaped to keep the cooking temperature Tg. To the associated heat storage 1 However, no voltage is applied so that they are against the radiator 53 and 54 as well as against the cooking space 52 are thermally insulated (second program section P2).

At the first part of the cooking section is followed by a second part from the time tb, which lasts to an end of the cooking section at a time te (cooking time). During this second part are the radiators 53 and 54 disabled or off, the heat storage 1 however, activated or voltage applied (third program section P3). This can heat from the heat storage 1 to the cooking chamber 52 be discharged, so that this without energizing the radiator 53 and 54 until the end of the cooking time at te can be kept substantially at the cooking temperature Tg.

Of course, the present invention is not limited to the embodiments shown.

LIST OF REFERENCE NUMBERS

1

heat storage

2

Heat storage material

3

Teflon sheet

4

electrode

5

Area of the Teflon layer

6

remaining area of the Teflon layer

7

outer location

8th

receiving part

9

cover

10

casing

11

Part of the housing

20

Heat generating unit

21

heat storage

25

Area

29

cover

32

deepening

33

Heat generating element

34

electrically insulating layer

40

oven

52

oven

53

Top heat radiator

54

Bottom heating element

55

upper oven wall

56

lower oven wall

57

control unit

t

Time

t0

Start time

Tg

Oven temperature

Tr

room temperature

ta

time

tb

time

th

end of cooking time

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19824172 A1 [0002]

Claims (14)

Heat storage ( 1 ; 21 ) for a household heat treatment device ( 40 ), characterized in that the heat storage ( 1 ; 21 ) in a housing ( 10 ) accommodated heat storage material ( 2 ) and a thermal conductivity of at least a part of the housing ( 10 ) is adjustable. Heat storage ( 1 ; 21 ) according to claim 1, characterized in that the thermal conductivity is adjustable by means of applying an electrical voltage. Heat storage ( 1 ; 21 ) according to claim 1, characterized in that the electrical voltage is not more than about 24 V, in particular not more than about 12 V is. Heat storage ( 1 ; 21 ) according to one of the preceding claims, characterized in that the heat storage material ( 2 ) comprises a mixture of graphite and aluminum. Heat storage ( 1 ; 21 ) according to one of the preceding claims, characterized in that the housing ( 10 ) at least one layer ( 3 . 5 ) having an adjustable thermal conductivity, wherein the at least one layer ( 3 . 5 ) the heat storage material ( 2 ) at least partially surrounds. Heat storage ( 1 ; 21 ) according to one of the preceding claims, characterized in that the at least one layer ( 3 . 5 ) with the adjustable thermal conductivity at least one electrode ( 4 ) having. Heat storage ( 1 ; 21 ) according to one of claims 5 to 6, characterized in that at least one layer ( 3 . 5 ) having the adjustable thermal conductivity teflon, perlite and / or ceramic fiber. Heat storage ( 1 ; 21 ) according to claim 7, characterized in that the position ( 3 . 5 ) having the adjustable thermal conductivity at least two layers of Teflon, pearlite and / or ceramic fiber, between which the at least one electrode ( 4 ), and each of the layers has a layer thickness of about 1 mm. Heat storage ( 1 ; 21 ) according to one of the preceding claims, characterized in that the housing ( 10 ) an outer layer ( 7 ) of a highly thermally conductive material, in particular copper and / or aluminum. Heat generating unit ( 20 ), comprising at least one heat-generating element ( 33 ), characterized in that the heat generating unit ( 20 ) at least one heat storage ( 21 ) according to one of the preceding claims. Household heat treatment device ( 40 ), characterized in that the household heat treatment device ( 40 ) at least one heat storage ( 1 ) according to one of claims 1 to 9 and at least one heat-generating element ( 53 . 54 ) or at least one heat-generating unit ( 20 ) according to claim 10, and the household heat treatment device ( 40 ) also at least one control unit ( 57 ), wherein the at least one heat storage ( 1 ) for adjusting its thermal conductivity with the control unit ( 57 ) is functionally connected. Household heat treatment device ( 40 ) according to claim 11, characterized in that the control unit ( 57 ) has a program control, which is adapted to: - in a first program section (P1) the at least one heat-generating element ( 53 . 54 ) and the thermal conductivity of the part ( 11 ) of the housing ( 10 ), whose thermal conductivity is adjustable, to set to a comparatively high value, in particular by applying an electrical voltage; In a second program section (P2), the at least one heat-generating element ( 53 . 54 ) and the thermal conductivity of the part ( 11 ) of the housing ( 10 ) whose thermal conductivity is adjustable to a comparatively low value; and - in a third program section (P3) the at least one heat-generating element ( 53 . 54 ) and the thermal conductivity of the part ( 11 ) of the housing ( 10 ), whose thermal conductivity is adjustable, to set to a comparatively high value, in particular by applying an electrical voltage. Household heat treatment device ( 40 ) according to claim 12, characterized in that an amount of heat required for carrying out the third program section to a from the at least one heat storage ( 1 ) corresponds to the maximum amount of heat that can be delivered. Method for operating a household heat treatment device ( 40 ), characterized in that the household heat treatment device ( 40 ) at least one heat storage ( 1 ; 21 ) and at least one heat generating element ( 33 ; 53 . 54 ), which in a housing ( 10 ) accommodated heat storage material ( 2 ), wherein a thermal conductivity of at least one part ( 11 ) of the housing ( 10 ) is adjustable, and where In a first program section (P1) the at least one heat-generating element ( 33 ; 53 . 54 ) and the thermal conductivity of the part ( 11 ) of the housing ( 10 ), whose thermal conductivity is adjustable, is adjusted to a comparatively low value, in particular by applying an electrical voltage; In a second program section (P2), the at least one heat-generating element ( 33 ; 53 . 54 ) and the thermal conductivity of the part ( 11 ) of the housing ( 10 ), whose thermal conductivity is adjustable, is set to a comparatively high value; and - in a third program section (P3) the at least one heat-generating element ( 33 ; 53 . 54 ) and the thermal conductivity of the part ( 11 ) of the housing ( 10 ), whose thermal conductivity is adjustable, is set to a comparatively low value, in particular by applying an electrical voltage.

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