DE102019116525A1 - Thermal buffer storage, process for its manufacture and process for its operation - Google Patents

Abstract

In order to be able to efficiently operate a buffer storage (1), in particular as a layer buffer storage for a low-energy house or zero-energy house, optimizations are carried out by replacing the layered panels with panels (5) made of metal foam, which also serve as heating elements (5) and are photovoltaic generated electricity heat the storage fluid (100) in the buffer storage (1), at the same time limit the vertical flow, - electrical auxiliary heater (14) outside the buffer storage on the inlet or outlet line (9a, b) are provided for the domestic water, especially in the Form as an inductive electrical heating element (14), - to improve the heat retention capacity, a latent heat storage material (15) is optionally arranged in the interior of the buffer store (1).

Description

field of use

Thermal buffer storage tanks are used to supply living spaces with heating and hot water, as their storage fluid can be heated from different connected energy sources and supplies different heat consumers such as heating or hot water consumers with different temperature levels with heat.

Technical background

In order to have storage fluid with the highest possible temperature level available within the buffer storage, this is usually designed as a stratified buffer storage by providing inlet openings and drainage openings corresponding to different temperature levels at different heights with the aim of temperature stratification in the buffer storage to generate, and to maintain this as well as possible when supplying and removing storage fluid.

For this purpose, so-called layered plates are installed horizontally across the free cross-section of the storage space in such layered buffer storage tanks, which have passages of a defined, limited number and size in order to control and limit vertical flows in the storage space and the temperature stratification as best as possible.

Up to now, such buffer storage has been regenerative, among others. heated for example by means of a heat transfer fluid heated by a thermal solar collector.

Newer low-energy houses or zero-energy houses often do without a thermal solar collector for cost reasons and because of the structural effort, but have a photovoltaic system, the electricity of which is preferably consumed by the residents - if necessary after intermediate storage in a separate buffer -Battery - but if there is excess electricity and the buffer battery is full, it must be used for other purposes.

In addition to feeding into the public power grid, which is of little economic interest, it is also possible to heat the thermal buffer storage tank using excess electricity.

For this purpose, among other things, electrical heating elements, so-called heating cartridges or heating blades, are known, which protrude from the outside into the storage space of the thermal buffer storage unit for its heating.

However, these electrical heating elements are usually equipped as a simple resistance heater with an electrical conductor approximately as thick as a finger, coiled at most a few times, and have only a small surface area.

For this reason, on the one hand, the heating output is low, especially with low currents, and on the other hand, the heat value of the water heated as a result - which is usually used as storage fluid - is not positively influenced by this, and thus also not the holding time for which the storage is -Fluid - despite the existing thermal insulation of the shell of the buffer storage tank - can hold the stored heat.

Furthermore, the case can arise that at a relatively low temperature level in the buffer storage, the required domestic water, e.g. for showering - which usually takes place in the buffer tank by means of a heat exchanger there - cannot take place quickly enough according to the desired throughput of the shower and requires additional electrical heating, which heats the domestic water, preferably downstream of the buffer tank, to the set temperature.

Presentation of the invention

Technical task

It is therefore the object of the invention to provide a thermal buffer store, in particular also for the operating mode of a stratified buffer store, which is simple and inexpensive and easy to optimize, as well as ensuring high efficiency in operation.

Solution of the task

This object is achieved by the features of claims 1, 12 and 16. Advantageous embodiments emerge from the subclaims.

With regard to the buffer storage, this object is achieved in that the electrical heating element arranged in the storage space of the buffer storage has a surface-to-volume ratio of at least 100 m ² / m ³ , better at least 400 m ² / m ³ , better at least 800 m ² / m ³ , having.

Due to the large contact area with the surrounding storage fluid compared to the ground and thus also the space required by the heating element, rapid heating of the storage fluid is possible even at low currents applied to the electrically conductive parts of the heating element, as is typically provided by a photovoltaic system will be made available. For this purpose, the heating element consists at least partially of metal, preferably of copper or aluminum, since these are inexpensive materials that have high electrical conductivity and thermal conductivity.

The electrical heating element preferably has an open-pore structure, it being possible in particular to be an open-pore foam, in particular a metal foam. The number of pores is preferably at least 5 , better at least 10 , better at least 20th Pores per linear inch (PPI).

In particular, this also makes it possible to keep the pressure loss that occurs when there is a flow through such an, in particular open-pored, heating element. The pressure loss when flowing through the heating element should preferably be below 20% at a pressure of 1.0-4.5 bar overpressure, and especially when flowing through the storage fluid such as water over a flow path of 5 cm.

The dimensioning parameters of the heating element and the storage fluid should preferably be chosen so that the thermal conductivity of the heating element, the cavities or spaces of which are filled with the storage fluid, is at least 1.0 W / mK, better still at least 2.0 W / mK, better at least 3.0 W / mK. This ensures rapid heating of the storage fluid when power is applied to the electrical heating element.

If the open-pore structure is an open-pore foam, this preferably consists of a plastic, especially polyurethane, which is coated with an electrically conductive material, in particular metal, in particular copper, or in which the open-pored foam consists of a plastic that is itself electrically conductive . In the case of a coating with an electrically conductive material, it has proven to be advantageous that its layer thickness is a maximum of 2.5 mm, better a maximum of 2.0 mm, better a maximum of 1.0 mm and / or a minimum of 200 μm, better a minimum of 400 μm, better a minimum of 800 µm, especially in the case of a foam with 10 Pores per linear inch (PPI).
In particular, the non-conductive material, in particular plastic, is removed after the coating and before the use of the open-pored foam, in particular by burning out.

This obviously represents the right compromise between thermal conductivity and thermal capacity of the electrical heating element.

The open-pore structure can also consist of a bonded or sintered metal powder with cavities between the individual grains of the powder.

The open-pore structure can also consist of a lattice structure produced in a defined manner, which can be produced in particular by means of an iterative process in which the optimal dimensioning parameters of the open-pore structure for the respective application can be achieved.

In order to heat the open-pore structure of the electrical heating element, electrical heating wires are preferably inserted into the open-pore structure, which should in particular have a thickness of at least 0.5 mm in diameter, and which are electrically conductively connected to the electrically conductive material of the open-pore structure and / or are thermally connected.

By means of an electrically conductive connection, a current can flow from the electrical heating wires into the metallic coating and, as a result, it can be heated by the electrical resistance.

However, should the current flow completely or primarily through the electrical heating wires and these heat up due to their electrical resistance - which can be achieved by choosing the length and cross section as well as the material of the heating wires in relation to the introduced current and its current strength - the thermally conductive parts of the open-pored structure, in particular likewise its electrically conductive coatings, completely or primarily heated by thermal means of the heated heating wires. In order to avoid short circuits, there is usually electrical insulation between the heating wires and the other electrically conductive parts of the heating element, for example the electrically conductive coating.

Another solution is to apply current directly to the electrically conductive part of the open-pored structure, i.e. in particular the electrically conductive coating, by having corresponding power connections on opposite sides of the open-pored structure, with the largest possible contact areas between the power connections and the electrically conductive part the open-pored structure are necessary.

Particularly when high voltages are applied, there is a risk that hydrogen will be produced through electrolysis. In order to avoid the associated risk of explosion, a platinum catalyst can be used at the highest point of the storage tank to neutralize the hydrogen gas, by means of an oxidative chemical Process of converting hydrogen into water immediately.

Preferably, each of the electrical heating elements is plate-shaped and extends in an approximately horizontal direction in the storage space, and over at least 80%, better at least 85%, better at least 90%, better at least 95%, better at least 98% of the free inner horizontal cross-section of the Storage space at the location of the plate-shaped heating element.

The electrical heating element is preferably attached in an electrically insulated manner with respect to the shell of the storage space, in particular if it consists of an electrically conductive material, in order to reliably prevent current flow into the shell here.

In order to optimize the heat storage capacity with unchanged volume, the storage fluid used is preferably heavily or completely demineralized, for example distilled, water, especially ultrapure water, and / or water with an electrical conductivity δ below 1.0 μS / m, better below 0.065 µS / m, in particular at 25 ° C in each case.

A heat exchanger is preferably present in the storage space of such a buffer tank, in particular in the form of a helical pipe section, a so-called pipe coil, which runs into the shell of the buffer tank with an inlet opening and out of it again with an outlet opening. Service water is passed through this heat exchanger and heated by means of the storage fluid, and the drain opening is in connection with the potential hot water consumers, such as a shower, in a building.

In the event that the temperature level in the buffer tank is not high enough to achieve the desired target temperature of the domestic water or not to achieve it in a desired short time, an electric auxiliary heater on the inlet line or outlet line, preferably on the inlet line, can be installed Heat exchanger, so preferably outside of the storage space, be arranged.

For example, as a method for operating such a buffer tank on the drain line, the temperature of the domestic water - usually controlled by a sensor - can drop below a typical shower temperature of 45 ° C, either because the temperature in the buffer tank is already relatively low or because Due to the large amount of domestic water withdrawn per unit of time, it cannot be heated up quickly enough to the desired temperature on the way through the coil.

If the actual temperature measured at the outlet of the domestic water from the buffer tank is too low, the control switches on the electrical auxiliary heater on the inlet line and controls it so that the desired target temperature of the domestic water is reached at the outlet. The additional heating at the inlet prevents the storage fluid from giving off additional heat to the pipe coil and cooling down further, and thereby falling below a desired minimum temperature in the storage fluid, as is required, for example, for operating the underfloor heating of the building.

This temperature of the storage fluid is also preferably measured and taken into account in the control of the auxiliary heater, which would be possible, for example, by partially closing a valve, in particular a proportional valve, on the inlet line or outlet line.

Because if the temperature in the storage fluid is above the desired minimum temperature, the flow time through the coiled pipe, i.e. the heat exchanger, can be increased in this way at the expense of the amount of water withdrawn per unit of time, and electrical additional heating can therefore be dispensed with .

According to the invention, such an electrical auxiliary heater consists of an induction heating element which can heat the supply line or drain line, which consists of an electrically conductive material, by means of induction. A section of the inlet line or the outlet line is preferably surrounded by an electrical coil - which may optionally consist of high-temperature conductors or superconductors - which, however, preferably has no electrically conductive contact with the inlet line or outlet line, but is preferably arranged at a small distance around them becomes.

In this way, the material of the supply line or drain line is heated, possibly theoretically to a red-hot state, and very quickly heats the service water flowing through it.

In order to achieve a compact design of the inductive heater, the inlet line or outlet line to be heated also has the shape of a helix, but with straight sections, especially in each turn of the helix, around which the electrical coil can be arranged particularly easily.

In particular, the inside of the supply line or drain line can be filled with an open-pore structure made of a ferromagnetic metal, in particular a metal foam, which can either be conventionally heated by inserted electrical heating wires, or also by means of electrical induction using an induction coil placed around the line.

In order to increase the heat capacity of the buffer store and in particular to improve its heat retention capacity, a latent heat storage medium can also be present in the storage space, which is able to store heat over a long period of time and with almost no loss. In particular, so-called phase change materials (PCM) are used for this purpose, which change their phase state when passing through a defined temperature threshold, for example solidify, and thereby absorb large amounts of energy. For the temperature level between 0 ° C. and 100 ° C. that prevails here, for example, paraffin or sodium acetate trihydrate is suitable as such a phase change material.

Depending on the chemical nature of this phase change material, it can be in direct contact with the storage fluid and placed in the storage space without its own casing, or it can be accommodated in a closed container which, however, must be in thermal contact with the storage fluid should then have the largest possible surface area compared to the storage fluid.

With regard to the method for producing such a buffer store, the parameters of the electrical heating element in the interior of the buffer store, in particular its solids content and / or pore content and / or its pore size and / or its pore arrangement and / or the size of the smallest free cross-sections, their pore connections and / or the shape of the heating element and / or the size of the heating element and / or the positioning of the heating element in the storage space can be determined as a function of parameters of the buffer storage, in particular its dimensions of the free interior space and / or volume and / or the arrangement of supply opening and drain opening and / or the arrangement of the inlet opening and the outlet opening and / or the size of these openings and / or the intended operating parameters of the buffer storage that the heat capacity and / or the heat retention capacity and / or the rate of temperature change for the intended application t of the storage fluid in the buffer storage is optimized. Such an optimization is preferably carried out by means of a computer simulation.

If the electrical heating element is an open-pore structure in the form of an open-pore foam or open-pore latticework, this open-pore structure, in particular its supporting structure, is preferably produced in an iterative production process such as 3-D printing. If necessary, the obvious heating element can also be produced directly in this way without a support structure.

• Bei einem Verfahren wird das Heizelement durch Wickeln einer dreidimensional strukturierten Blechfolie hergestellt, insbesondere durch Wickeln einer gewellten Blechfolie um eine Wickelachse parallel zur Verlaufsrichtung der Erhöhungen oder Vertiefungen der gewellten Blechfolie. Der entstehende Wickel oder auch Wabenkörper genannt ist dann von der einen zur anderen Stirnseite entlang der durch die Wellung gebildeten Kanäle frei durchströmbar, bietet aber wegen des Kanal-Querschnitts bis herunter auf weniger als 1 mm² eine hohe Oberfläche in Form der Kanalwände.

The support structure can be coated with an electrically conductive material in different ways, for example by means of galvanic coating or by deposition of the metal from the gas phase (CVD) or by immersing the support structure with the so-called dip-coating process or another Process which produces a homogeneous surface coating, in particular with a constant layer thickness.
A heating element with a large surface, i.e. contact area with a surrounding medium, in relation to its volume can, however, also be produced in other ways, possibly more cost-effectively than the previously described methods:

• In one method, the heating element is produced by winding a three-dimensionally structured sheet metal foil, in particular by winding a corrugated sheet metal foil around a winding axis parallel to the direction of the elevations or depressions of the corrugated sheet metal foil. The resulting winding or also called honeycomb body can then be freely flowed through from one end to the other along the channels formed by the corrugation, but due to the channel cross-section it offers a high surface area in the form of the channel walls down to less than 1 mm ² .

In another method, the heating element is produced by producing a tangle of very long, very thin metal fibers with many mutual contact points, the metal fibers being produced, for example, by planing a metal wire with a cross section of several mm ² in its longitudinal direction.

This tangle is then in particular solidified, in particular glued and / or welded and / or held together in a permeable housing.

Figure list

• 1: einen erfindungsgemäßen Pufferspeicher im Vertikalschnitt
• 2: den Pufferspeicher gemäß 1a im Horizontalschnitt geschnitten entlang der Linie II - II

Embodiments according to the invention are described in more detail below by way of example. Show it:

• 1 : a buffer memory according to the invention in vertical section
• 2 : the buffer according to 1a in horizontal section along the line II - II

• Wie jeder gattungsgemäße, bekannte Pufferspeicher besitzt auch dieser Pufferspeicher 1 zunächst eine - thermisch möglichst gut, beispielsweise mittels Vakuum wie in 2 angedeutet, isolierte - Hülle 2, die den Speicherraum 1* umschließt, in dem es eine Zufuhr-Öffnung 3 an einer tief liegenden, insbesondere der am tiefsten liegenden, Stelle des Speicherraumes 1* und eine Abfuhr-Öffnung 4 an einer hoch liegenden Stelle durch die Hülle 2 hindurch gibt zum Zuführen und Abführen von Speicher-Fluid 100 in den Speicherraum 1*, den Betrieb des Pufferspeichers 1 vorzugsweise vollständig mit dem Speicher-Fluid 100 gefüllt ist.

The vertical section of the 1 leaves the essential elements of the buffer memory 1 detect:

• Like every generic, known buffer memory, this one also has a buffer memory 1 first one - thermally as good as possible, for example using a vacuum as in 2 indicated, insulated - shell 2 who have made the storage space 1* encloses in which there is a feed opening 3 at a low-lying, in particular the lowest-lying, point of the storage space 1* and a discharge opening 4th at a high point through the envelope 2 through there for supplying and removing storage fluid 100 in the storage room 1* , the operation of the buffer storage 1 preferably completely with the storage fluid 100 is filled.

In order to keep the surface small and a vertical temperature stratification in the storage space 1' to enable is the buffer storage 1 Usually an upright cylinder with a rounded or even spherical upper and lower end, the height of which is vertical 10 is significantly greater than its transverse extent in one of the transverse directions in 11.1 , 11.2 .

As is also known, at a certain altitude - here about halfway up - there is one, especially around the vertical 10 coiled, helix from a pipe as a heat exchanger 8th in the storage space 1* , their inlet pipe 9a and drain line 9b through a corresponding inlet opening 8a and a drain opening 8b through the shell 2 extend through it so that it is inside the pipe coil 8th flowing domestic water to be heated is not in direct contact with the storage fluid 100 is, but only in thermal contact via the material of the pipeline of the heat exchanger 8th .

The peculiarities according to the invention consist on the one hand in the fact that they are often in a known buffer memory 1 vertically permeable, so-called layered plates arranged at a distance one above the other, lying approximately horizontally, here as electrical, plate-shaped heating elements 5 are formed, which can be electrically heated and also vertically for the storage fluid 100 are permeable, but have a very high surface area compared to their mass.

These plate-shaped electrical heating elements, here three on top of one another, usually consist of an open-pored metal structure, in particular metal foam, and extend essentially over the entire horizontal cross section of the storage space 1* .

• Entweder gemäß einer 1. Variante mittels der hier in den beiden oberen Platten dargestellten, in das elektrische Heizelement 5 eingelegten, elektrischen beheizbaren Heizdrähte 6, die insbesondere nur thermisch, aber nicht elektrisch leitend, mit der offenporigen Metallstruktur verbunden sind.

They can be heated electrically in different ways:

• Either according to a first variant by means of the one shown here in the two upper plates, in the electrical heating element 5 inserted, electrically heated heating wires 6th which are connected to the open-pored metal structure in particular only thermally, but not electrically.

Or according to a second variant, as shown in the case of the bottom plate, by applying the metal foam, for example 5 On the edge, preferably only on opposite sides, electrically conductive contact strips making contact 5a with electrical current, which is in electrically conductive contact on the one hand with the metal foam, for example, which it surrounds, and on the other hand with the electrical power connections 7a , 7b that are electrically isolated by the shell 2 are brought in from the outside.

In a buffer tank 1 only one of the two variants can be used or both, as exemplified in 1 shown.

It is also connected to the inlet line 9a of the heat exchanger 8th an electric auxiliary heater for the domestic water 13 arranged, here in the form of a pipe section of the inlet line 9A around, at least in sections, arranged electrical coil 14th of the heater 13 in order to heat the pipe section consisting of electrically conductive and / or magnetizable material by means of electrical induction. Alternatively, a flow-through structure made of electrically conductive and / or magnetizable material, such as a metal foam, arranged in the interior of this pipeline section could also be heated in this way by means of electrical induction, so that the material of the supply line then does not have to be electrically or magnetically conductive . A.

For this purpose, the pipeline section can be designed to be coiled as shown, but preferably with straight sections in order to facilitate the attachment of the electrical coil.

Furthermore is in the storage space 1* Latent heat storage material 15th arranged, preferably housed in a surrounding container 16 made of thermally conductive material such as sheet metal, which is heated by the surrounding storage fluid 100 A phase transition of the latent heat storage material can store a large amount of heat and over a very long period of time.

This material 15th or the container 16 with this material 15th it is preferably in the upper area, in particular in the upper half of the storage space 1* , especially above the heat exchanger 8th , arranged while the electrical heating elements 5 in the form of plates made of, for example, metal foam, preferably in the lower half of the storage space 1* , preferably under the heat exchanger 8th , are arranged.

• Dabei Ist ersichtlich, dass trotz des runden horizontalen Querschnitts der Hülle 2 die Platte 5 in der Aufsicht betrachtet nicht rund, sondern polygon, vorzugsweise quadratisch oder auch 6-eckig oder 8-eckig, ist, um den Verschnitt bei der Herstellung aus einer größeren Roh-Platte zu vermeiden angesichts der hohen Kosten der Herstellung dieses Materials.

1b shows the lowest electrical heating element 5 with the contact strips placed on both sides 5a , b in horizontal section:

• It can be seen that despite the round horizontal cross-section of the shell 2 the plate 5 When viewed from above, it is not round, but polygonal, preferably square or also hexagonal or octagonal, in order to avoid the waste when producing from a larger raw board in view of the high costs of producing this material.

In order to achieve a bypass flow of the storage fluid 100 vertically on the plate 5 over to avoid the the temperature stratification in the buffer memory 1 would affect is the distance between the outer edge of the plate 5 and the surrounding envelope 2 by in particular at an angle from the shell 2 to the plate 5 rising baffles 18th locked.

List of reference symbols

1

Buffer storage

1*

Storage space

2

Shell

3

Feed opening

4th

Discharge opening

5

electric heating element

5a

electrical contact strips

6th

electric heating wire

7a, b

Power connection

8th

Heat exchanger

8a

Inlet opening

8b

Drain opening

9a

Inlet pipe

9b

Drain line

10

vertical

11

1. horizontal transverse direction

12

2. horizontal transverse direction

13

electric auxiliary heater

14th

electric coil

15th

Latent heat storage material, paraffin

16

container

17th

Spiked plate

17a, b

needle

18th

Baffle

19th

20th

100

Storage fluid

Claims (16)

Thermal buffer storage (1) for heating a storage fluid (100) located in its storage space (1 *) and storing its thermal energy, with - a thermally insulated shell (2) surrounding the storage space (1 *), - a supply -Opening (3) and a discharge opening (4) for storage fluid (100) in the storage space (1 *), - at least one electrical heating element (5) in the storage space (1 *) for heating the storage fluid, characterized that the ratio of surface to volume of the heating element (5) is at least 100 m ² / m ³ , better at least 400 m ² / m ³ , better at least 800 m ² / m ³ . (Physical Properties) Buffer storage after Claim 1 , characterized in that - the heating element (5) consists at least partially of metal and / or - the pressure loss when the storage fluid (100) flows through the heating element (5) at a pressure of 1.0-4.5 bar overpressure and a flow path of 5 cm is below 20%, and / or - the thermal conductivity of the heating element (5), in particular including the cavities filled with the storage fluid (100), in particular at least 1.0 W / mK, better at least 2, 0 W / mK, better at least 3.0 W / mK, and / or - the heating element (5) is an open-pore structure, in particular an open-pore foam, in particular with a number of pores of at least 5, better at least 10, better at least 20 Pores per linear inch (PPI). (1st variant) Buffer storage according to one of the preceding claims, characterized in that - the open-cell foam, at least in an intermediate step during its production, is made of an electrically non-conductive carrier material, in particular plastic, in particular polyurethane, whose surface, in particular its entire surface, is coated with a very good thermally conductive and / or electrically conductive coating material, in particular metal, in particular copper, - in particular the non-conductive carrier material, in particular plastic, according to the Coating and is removed before the use of the open-pored foam, in particular by burning out, - in particular the layer thickness of the thermally and / or electrically conductive coating material is a maximum of 2.5 mm, better a maximum of 2.0 mm, better a maximum of 1.0 mm and / or, - in particular the The layer thickness of the coating material is a minimum of 200 μm, better a minimum of 400 μm, better a minimum of 600 μm, better a minimum of 800 μm, in particular in the case of a foam with 10 pores per linear inch (PPI). Buffer memory according to one of the preceding claims, characterized in that electrical heating wires (6), in particular with a thickness of at least 0.5 mm diameter, are embedded in the open-pore structure, in particular the open-pore foam, which are coated with the highly thermally conductive coating material of open-pored structure are thermally conductively connected, but are preferably electrically insulated from it. (2nd variant) Buffer storage according to one of the preceding claims, characterized in that - the open-pored structure consists of a, in particular pressed, glued or sintered, block of metal powder or metal chips, - in particular the metal is a mixture or an alloy of 60-90%, better 75 -85%, nickel and / or 10-40%, better 15-25%, is chromium. Buffer memory according to one of the preceding claims, characterized in that - on the electrically conductive material, in particular the coating material, the open-pored structure on opposite sides, in particular horizontally opposite sides, their greatest direction of extent, power connections (7a, b) are arranged and / or - several adjacent heating elements (5), in particular jointly operated by the application of current, in particular open-pore structures, are connected to one another in an electrically conductive manner by needles made of electrically conductive material penetrating into them on both sides. (Arrangement) Buffer storage according to one of the preceding claims, characterized in that - the heating element (5) is designed as a plate (5) and this extends in an approximately horizontal direction over at least 70%, better at least 80%, better at least 90%, better at least 95% , better at least 98% of the free inner horizontal cross-section of the storage space (1 *) extends, - in particular the plate (5) consists of several sub-plates (5a, b) lying on top of one another, between which a spiked plate (17) of good electrically conductive Material is arranged which has needles (17a, b) extending into both the overlying and the underlying partial plate (5a, b) which are attached to the, in particular, lattice-shaped spiked plate (17) and / or - the heating element ( 5) is attached electrically isolated from the shell (2). (Domestic hot water auxiliary heating) Buffer storage according to one of the preceding claims, wherein - in the storage space (1 *) a heat exchanger (8), in particular a helical pipe section (8), is arranged with an inlet opening (8a) and an outlet opening (8b) on the outside of the shell (2) - an electric auxiliary heater (13) is arranged outside the casing (2) on the inlet line (9a) or the outlet line (9b) to the inlet opening or outlet opening, characterized in that - the electric auxiliary heater (13) after the induction The principle works and the metal drain line (9b) or preferably the supply line (9a) heats up, in particular by isolating and / or spacing a section of the supply line (9a) or drain line (9b) from an electrical coil (14), in particular electrically , is surrounded. Buffer storage according to one of the preceding claims, characterized in that - the inlet line (9a) or outlet line (9b) to be heated is designed as a helix, - in particular each turn of the helix has two straight, preferably parallel to one another, sections around which the electrical coil (14) of the induction heater (13) is arranged. (Latent heat storage material) Buffer storage according to one of the preceding claims, characterized in that - a latent heat storage medium (15) is contained in the storage space, - in particular a phase change material (PCM) which, when passing through a defined temperature threshold, the phase state with energy absorption or energy release changes, especially paraffin (15). Buffer storage according to one of the preceding claims, characterized in that the latent heat storage material (15) - is either in direct contact with the storage fluid (100), - or is held in a closed container (16) which is thermally Contact with both the storage fluid (100) as well as with the latent heat storage material (15). A method for producing a buffer store, in particular according to one of the preceding claims, characterized in that - parameters of the heating element (5), in particular solid content and / or pore content and / or pore size and / or pore arrangement and / or size of the pore connections and / or shape of the heating element (5) and / or size of the heating element (5), depending on parameters of the buffer storage (1), in particular its dimensions and / or volume and / or arrangement of inlet and outlet and / or size of inlet and the sequence and / or the intended operating parameters of the buffer memory (1) are defined, in particular optimized by means of a computer simulation. Procedure according to Claim 12 , characterized in that - the heating element (5) itself or its electrically non-conductive support structure, if present, is produced in an iterative manufacturing process, - in particular according to the determined optimal parameters for the heating element (5), - in particular the support structure, e.g. galvanically is provided with a surface coating of metal - is provided with a surface coating of metal by means of CVD, - is provided with a surface coating of metal by means of dip-coating, - or by means of another method which produces a homogeneous surface coating, in particular with a constant layer thickness. Procedure according to Claim 12 , characterized in that the heating element (5) is produced by winding a three-dimensionally structured sheet metal foil, in particular by winding a corrugated sheet metal foil around a winding axis, parallel to the direction of the elevations or depressions of the corrugated sheet metal foil. Procedure according to Claim 12 , characterized in that the heating element (5) is produced by making a tangle of very long, very thin metal fibers with many mutual contact points, which is then especially solidified, especially glued or welded and / or held together in a permeable housing. Method for operating a buffer memory, in particular according to one of the preceding Claims 8 - 11 , characterized in that) if the actual temperature of the domestic water at the drain opening (8b) or drain line (9b) from the buffer tank (1) - either an auxiliary heater, in particular an electrically operated auxiliary heater (13) on the Domestic water line, in particular on the inlet line (9a), is activated in such a way that the desired target temperature of the domestic water in the drain line (9b) is reached and maintained, - or the domestic water flow rate is reduced per unit of time in particular by partially closing a valve on the inlet line (9a) or outlet line (9b), as long as the temperature of the storage fluid (100) is above a predetermined minimum temperature.

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