DE102017001169B4 - Heater for heating water and operating procedures - Google Patents

Abstract

Heater (2) for heating water (4),
- With a container (6) for filling with water (4), and
- With a heating element (12) in a filling state (F) of the container (6) at least partially in direct contact with the water (4), and
- With a water sensor (14) for determining a water temperature (TW) of the water (4) in the filling state (F), and
- With a controller (16) for operating the heating element (12) in the filling state (F) in dependence of the water sensor (14) determined water temperature (TW), characterized in that
- The heater (2) has a heating sensor (18) for determining a heating temperature (TH) of the heating element (12), and
- The controller (16) for operating the heating element (12) in the filling state (F) is also formed as a function of the heating sensor (18) determined heating temperature (TH),
the controller (16) contains at least one two-point controller (20, 22),
- The controller (16) includes a second two-step controller (22) for controlling an actual value (THI) of the heating temperature (TH) to a setpoint (THS) down, the only in the event that an actual value (TWI) of Water temperature (TW) is greater than a limit (G), the first two-step controller (20) is subordinate and otherwise inactive, wherein the second two-step controller (22) as a manipulated variable, a binary activation signal (A) for the heating element (12).

Description

The invention relates to a heater for heating water and a method for operating such a heater.

In various situations, it is desirable to heat or heat water. Such a need exists in particular on board aircraft, for example for the preparation of hot drinks or food or hot water z. B. on a hand wash or sink.

A heater for heating water is for example from the WO 2005/041 731 A2 known. The heater includes a container for filling with water, a heating element in an inlet zone of the container, a temperature sensor at the inlet zone and a controller for controlling the heating element using the information from the temperature sensor to maintain a predetermined temperature in the container.

From the DE 32 09 780 A1 a thermal limit switch for detecting the exceeding or falling below a predetermined level in a liquid container is known, which contains an electrically heated or cooled element, which is arranged at the level of the detected level. A temperature sensor responds to the temperature of the element. Another temperature sensor is located at the same height so that it responds to the ambient temperature. A temperature control arrangement receives the output signals of the two temperature sensors and seeks to maintain the temperature of the element at a value which deviates from the ambient temperature by a predetermined constant temperature difference. A threshold switch responds when the heating or cooling power supplied by the temperature control assembly to the element exceeds a certain threshold, thereby indicating the immersion of the element in the liquid.

From the DE 10 2008 059 060 A1 is a heatable, shell or trough-shaped and stationary built-in hot water tank, so for example a sink, a bathtub or the like, known, in which for heating a fillable medium, in particular water, a heating element is provided, in particular a heating element, with the medium on an induction basis can be heated, wherein in advantageous embodiments, limit and threshold values are monitored on the basis of which the heating element is automatically activated or deactivated, so that located in the process water tank medium can be maintained in a predetermined by the threshold and threshold temperature range.

From the DE 10 2008 049 277 A1 an electric heating system is known, in particular for a motor vehicle, which has at least one electric heater with at least one connected to a power source PTC heating element, and at least one device for continuously controlling the PTC heating element, wherein the at least one device for continuously controlling the PTC Heating element comprises a DC / DC converter, which regulates the heating power of the at least one PTC heating element. Furthermore, a method for continuously controlling an electric heating device is known, in particular an electric PTC heating device for a motor vehicle, which has at least one PTC heating element, wherein the voltage of the electric heating device is controlled by means of an output voltage of a DC / DC converter.

The object of the present invention is to improve the heating of water.

The object is achieved by a heater according to claim 1. Preferred or advantageous embodiments of the invention and other categories of invention will become apparent from the other claims, the following description and the accompanying drawings.

The heater is used for heating water and contains a container for filling with water. The heater contains a heating element. In a filling state of the container, the heating element is at least partially in direct contact with the water. The fill state is that state when the container is filled to a minimum fill level or higher with water. The heating element is then in contact with the water located inside the container or is surrounded by it.

The heater includes a temperature sensor for determining a temperature (called "water temperature") of the water in the container when it is in the fill state. The sensor is therefore called "water sensor". The heater contains a controller. The controller is used to operate the heating element as a function of the water temperature detected by the water sensor in the filling state.

The heater also includes another temperature sensor for detecting a temperature (called "heating temperature") of the heating element. This sensor is therefore called "heating sensor". The control is designed to operate the heating element in the filling state as a function of the heating temperature determined by the heating sensor. The controller thus operates the heating element as a function of the determined by the respective sensors Water temperature and depending on the heating temperature.

The controller is in particular a control or contains such. In this case, therefore, there is a feedback of the water temperature and / or the heating temperature to the controller in the sense of a control loop. The heating sensor is integrated in particular in the heating element to detect its temperature (heating temperature). The temperature sensor is especially in thermocouple.

Instead of the respective temperature, parameters which are correlated with the temperature and which can be deduced to the corresponding temperature can also be detected and optionally further processed. The water sensor is in particular a submersible sensor, which dips at least partially into the water in the container in the filling state of the container.

The invention has the advantage that not only the water temperature, but also the heating temperature of the heating element is detected and enters into the control of the heating element, the heating element can also be controlled so that adjusts to this a specific or desired heating temperature. In particular, if necessary, for example in a holding operation or in a final phase of the heating of the water before reaching a desired water temperature, the temperature of the heating element with respect to the heating temperature "uncontrolled" operation can be lowered. A lowering of the heating element temperature leads to a reduced calcification on the heating element and to an extended life of the heating element.

The controller contains at least one two-position controller. For such simple control tasks, such as the heating of service water, a two-point controller is usually sufficient and also easy and inexpensive to implement.

In a preferred variant of this embodiment, the controller includes a two-position controller, which serves to regulate an actual value of the water temperature to a desired value of the water temperature. The two-position controller has as a manipulated variable a binary activation signal for the heating element. With the help of the binary activation signal, the heating element is either turned off or not activated and thus performs no heating of the water or it is operated with a uniform "full power", for example, a nominal power. The corresponding operation takes place, for example, by applying a full supply voltage to an electrical resistance heating element, so there is no throttling, targeted PWM control (pulse-wide modulation), switching on a series resistor or the like. Thus, according to the binary enable signal, there is a simple change between operation and off-state (e.g., turn-on and turn-off) of the heating element. The supply voltage is, for example, the full vehicle electrical system voltage of an aircraft. Such a two-point controller is particularly easy to implement and leads to a total of a simple and inexpensive heater.

In a preferred variant of this embodiment, the desired value of the water temperature can be predetermined. On the heater can thus be specified, to which temperature to heat the water or at what temperature this is to be kept in operation. Usual here are, for example, two or more different predetermined temperatures between which can be selected on the device. For example, three different water temperatures of 43 ° C, 49 ° C and 54 ° C can be preselected or specified.

According to the invention, the above two-position controller is a first controller. The controller then contains a second two-position controller. This is used to control an actual value of the heating temperature to a setpoint of the heating temperature. This second two-position controller is subordinated to the first two-step controller only for a specific case, otherwise this is inactive, that is, the first two-step controller takes over the control task alone. The second two-step controller is then subordinated to the first, if an actual value of the water temperature is greater than a limit. The limit of the water temperature is less than the setpoint of the water temperature. The second two-position controller also has a binary activation signal for the heating element as the manipulated variable. In the inactive case, that is, when the water temperature is below the limit, the second two-position controller does not contribute to the control of the heating element, this is done solely from the first controller. The two activation signals are combined to form the heating element, in particular in the sense of an AND connection.

The area above the limit value represents either a holding operation or a last phase of heating water from the cold state. In this case, the second two-position controller is subordinate to the first two-position controller, which is why in this phase, the temperature of the heating element is adjusted to a desired value. The desired value of the heating temperature is in this case in particular smaller than that temperature of the heating element, which would normally be achieved by the second two-position controller without such a control. Above the setpoint of the water temperature, the heating element is deactivated again. This is in particular due to the superimposed first two-position controller ensured. According to this variant of the invention, therefore, first of all a powerful and rapid heating of water takes place up to the limit value by means of a comparatively hot heating element. In the last warm-up or warming phase, the temperature of the heating element is lowered to the setpoint of the heating temperature in order to protect the heating element and to reduce the calcification in this phase. Overall, this leads to a maintenance-free heater.

In a preferred variant of this embodiment, the limit value of the water temperature can be predetermined. As a result, an adjustment can be made or a desired compromise can be set between the effect of heating the water faster (higher limit value, subsequent reduction of the heating temperature, high heating power in the water) or saving the heating element more (lower limit, earlier reduction of the heating temperature, less Heating power in the water).

In a preferred variant of this embodiment, the limit value of the water temperature is selected as a function of the desired value of the water temperature. Thus, when the setpoint of the water temperature changes, the limit value also changes, without this having to be tracked separately. For example, the threshold is always selected a few Kelvin less than the set point of the water temperature, e.g. between 3K and 20K or 5K to 15K, in particular 10K smaller chosen. For example, the threshold may also be selected at a fixed percentage of the setpoint, for example between 50% and 95%, between 60% and 90%, or between 70% and 85%, especially 80%.

In a preferred variant of this embodiment, the desired value of the heating temperature can be predetermined. Thus, in particular, a heating temperature can be selected in which, in the corresponding operating case, there is still sufficient heating of the water, but also a desirably low calcification on the heating element. Here, too, a desired compromise can be chosen.

In a preferred variant of this embodiment, the desired value of the heating temperature is selected as a function of the desired value of the water temperature. For example, the set point of the heating temperature is selected to be a few Kelvin greater than the setpoint of the water temperature, e.g. by 1K to 20K or 3K to 10K or 5K to 7K, in particular 6 K. In this case, when a change in the setpoint of the water temperature, the setpoint of the heating temperature does not need to be tracked by hand, but is tracked automatically. Again, corresponding percentage ratios are possible from 100%, for example, the setpoint of the heating temperature is set to 101% to 130%, 105% to 120%, in particular 110% of the setpoint of the water temperature.

In a preferred embodiment, the heater includes a level sensor. The heating element can only be activated if the fill level sensor senses the filling state. This is an additional safety factor designed to prevent the heater from operating in the event of insufficient filling, which could result in dangerous overheating in the heater.

In a preferred embodiment, the heating element is an electrical resistance heating element. This is particularly suitable for the above-mentioned application scenarios, for example in an aircraft, is simple and easy to control, in particular by a two-position controller with a binary activation signal -. via a switch - connected to a voltage source or energy source or separable from this, for example, the electrical system of an aircraft.

In a preferred embodiment, the heater is a heater for an aircraft. The heater according to the invention is particularly suitable for use in aircraft, as this is simple and inexpensive and improved in terms of maintenance requirements compared to conventional heaters with non-controlled or controlled heating element temperature.

The object of the invention is also achieved by a method according to claim 11 for operating a heater according to the invention. The method and at least a part of its embodiments and the respective advantages have been explained analogously already in connection with the heater according to the invention. According to the method, the controller operates the heating element depending on the water temperature and the heating temperature. Mainly due to the consideration of the temperature of the heating element in the control, the above advantages arise.

The heating element is only activated if the actual value of the water temperature is lower than a setpoint. In this case, in addition, in the event that the actual value of the water temperature is greater than a limit value, the heating element is activated only if an actual value of the heating temperature is less than a desired value. The corresponding method has already been explained above in connection with the two-point controller, but is also feasible for any controller in a corresponding manner. The limit value for the water temperature is lower than the setpoint.

As a result, there is a temperature limitation or lowering the temperature of the Heating element in the warming operation or the last warm-up phase, as explained above. The desired value of the heating temperature is in this case in particular smaller than the temperature which would normally reach the heating element without such subordinate control of the heating temperature. Regardless of the control of the heating temperature is always a shutdown or deactivation of the heating element when the actual value of the water temperature exceeds the setpoint. For water temperatures between the limit value and the setpoint value, the lower-level control or regulation of the heating temperature is set to its setpoint value when the water temperature is superimposed on the setpoint.

In a preferred variant of this embodiment, the heating element is activated by being connected unregulated to a power source. Disconnecting from the source deactivates it accordingly. As explained above, this leads to a particularly simple control method, which can also be realized by two-point controller. The energy source is connected in binary to the heating element or separated from it. Otherwise, the heating element is in no way operated individually or regulated, for example by PWM, series resistors, current control during activation, etc.

In a preferred embodiment of the invention, the system is operated particularly safely by the heating element is always deactivated when the level sensor does not sense the filling or the heating sensor is a temperature above a critical value that never occurs at the intended water heating (eg 160 ° C. ), or the water sensor supplies a temperature which is above a critical value which never occurs during the intended heating of the water (eg 100 ° C.). So there is a triple safety shutdown of the heater.

The invention is based on the following findings, observations or considerations and still has the following embodiments. The embodiments are also called simplifying the "invention". In this case, the embodiments may also contain or correspond to parts or combinations of the abovementioned embodiments and / or optionally also include previously not mentioned embodiments.

The invention is based on the recognition that the main cause of the failure of water heaters is the overheating of the heating element due to limescale.

The basic idea of the invention is to prevent or reduce these calcium deposits as much as possible. This should be done by lowering the heating temperature in holding mode, based on a temperature measurement in the heating element.

The invention is based on the recognition that the essential task of a water heater (heater) is the provision of warm water at a predetermined temperature. By way of example, the following applies: The manipulated variable for temperature control is the current through the heating element. The setpoint, water temperature, is measured by an immersion temperature sensor. To prevent overheating in the water heater, a level sensor is integrated so that it is only heated when the tank is filled with water. The avoidance of overheating of the heating element is a safety-relevant function. Therefore, for redundancy reasons, in addition to the level sensor, a thermocouple (temperature sensor for temperature of the heating element) integrated into the heating element to monitor the heating element temperature. In the event of a fault (temperature> limit, for example 160 ° C), the heater (heating element) is switched off with this additional temperature information and overheating of the heating element is prevented.

The resulting information about the heating element temperature is also used to optimize the water temperature control so that a reduction of the calcification is achieved.

The water temperature control is a two-point control with a subordinate, switchable two-point controller for the heating element temperature. The heating element temperature control is activated as soon as the control deviation of the water temperature control falls below a defined threshold value (difference between limit value and setpoint of the water temperature). The setpoint for the heating element temperature is chosen so that the difference to the desired water temperature is as small as possible, but nevertheless the desired heating power is available for heating water.

When the actual temperature of the water exceeds the threshold (e.g., at least 10 ° K below the SET temperature of the water), the heater temperature control is activated and the heater is controlled to a set temperature value (e.g., 60 ° C). This control is active as long as the water temperature has not reached the set point. When the setpoint is exceeded, the two-point controller uses the water temperature control, which can be set in 3 stages, and switches off.

For example, without the control described, the heating element temperature would regularly rise above 80 ° C. The temperature of the heater is controlled by the heating element temperature control Heating element limited to about 60 ° C, whereby the lime growth in the water heater is minimized.

If the heating element were about 85 ° C hot without the heating element temperature control, it would become more calcified.

In addition to minimizing calcification, a further advantage is an increased service life, since the controller is less overshoot and thus the permanent stress of the heating element is reduced by the temperature changes.

According to the invention, this also results in an anti-lime control. The result is a water heating with adapted heating temperature to reduce limescale.

According to the invention, a longer service life or longer maintenance intervals for e.g. a decalcification with citric acid. According to the invention, the calcification is reduced by a hardware solution.

• 1 ein Heizgerät in einem Flugzeug,
• 2 einen Regelkreis für das Heizgerät aus 1,
• 3 einen Zeitverlauf verschiedener Größen a) in einem Heizgerät ohne zweiten Regler und b) gemäß der Erfindung,
• 4 die Zeitverläufe der Heiztemperatur der 3a und 3b,
• 5 die Zeitverläufe des Heizelementstromes der 3a und 3b.

Further features, effects and advantages of the invention will become apparent from the following description of a preferred embodiment of the invention and the accompanying figures. This shows in a schematic outline sketch:

• 1 a heater in an airplane,
• 2 a control circuit for the heater off 1 .
• 3 a time course of different sizes a) in a heater without a second regulator and b) according to the invention,
• 4 the time courses of the heating temperature of 3a and 3b .
• 5 the time courses of the Heizelementstromes the 3a and 3b ,

1 shows a heater 2 for heating water 4 , The heater 2 contains a container 6 for filling with the water 4 , The container 6 has an entrance 8th for supplying water 4 and an exit 10 for removing heated water 4 , where the direction of flow for the water 4 indicated by arrows. 1 shows the container 6 in a proper state of filling F so that this is sufficient with water 4 is filled for its operation.

The heater 2 contains a heating element 12 in the state of filling F in direct contact with the water 4 is, that is lapped by this. During operation or activation of the heating element 12 If this gets hot on its surface, it heats the water in contact with it 4 , The heater 2 contains a first temperature sensor in the form of a so-called water sensor 14 which determines a temperature, called water temperature TW of the water 4 in the filling state F serves. The heater 2 contains a second temperature sensor in the form of a so-called heating sensor 18 , This serves to determine a temperature, called heating temperature TH of the heating element 12 ,

The heater 2 also includes a controller 16 used to operate or drive the heating element 12 in the filling state F serves. The control 16 controls the heating element 12 depending on both the water temperature TW as well as the heating temperature TH at or is suitable or trained.

The control 16 contains a first two-position controller 20 , This regulates an actual value TWI the water temperature TW to a setpoint TWS the water temperature TW in. The manipulated variable is the first two-position controller 20 this is a binary activation signal A for the heating element 12 on. The setpoint TWS is specifiable and in the present case 54 ° C. Alternatively, the values 49 ° C or 43 ° C can be selected (three heat levels).

The control 60 also contains a second two-position controller 22 , This regulates an actual value THI the heating temperature TH to a setpoint THS in. The second two-position controller 22 is the first two-position controller 20 However, just in case subordinate that the actual value TWI the water temperature TW greater than a limit G is. Otherwise, the second two-position controller 22 switched inactive and the control of the heating element 12 takes place solely via the first two-position controller 20 ,

Because the second two-position controller 22 if necessary, the first two-position controller 20 is subordinate, is the second two-step controller 22 only as long as for the control of the heating element 12 relevant as long as the actual value TWI less than the setpoint TWS is. In this case, the first two-position controller switches 20 the heating element 12 inactive or deactivates this and "overrules" the second two-position controller 22 , Also the second two-position controller 22 has a corresponding binary activation signal as the manipulated variable A on. The two manipulated variables of the first and second two-level controller 20 . 22 are merged in the sense of an AND link.

The limit G for the water temperature TW is here again specifiable, but here depending on the setpoint TWS selected and therefore above the setpoint TWS selectable. In the example, the limit is G 10K less than the setpoint TWS and is therefore 44 ° C. The nominal value THS the heating temperature can also be specified, but in the example also dependent on the setpoint TWS namely 6 K larger than this, that is 60 ° C. Again, the default is done by selecting the setpoint TWS , For other setpoints TWS limit will shift G and setpoint THS corresponding.

As a safety criterion, the heater contains 2 a level sensor 24 that the fill state F either sensed or not. In the present case there is enough water 4 filled so that the filling state F is sensed. A safety circuit in the controller 16 causes the heating element 12 anyway only activated if the filling state F from the level sensor 24 is sensed. The heating element 12 is an electrical resistance heating element.

The heater 2 is a heater in an aircraft, not shown 30 and is installed in the intended state of installation as on-board unit in the aircraft. The heating element 12 is via a switching element 26 to an energy source 28 connected, here the electrical system of the aircraft 30 , The switching element 26 knows only two switching states, which is why the heating element 12 either with its corresponding currently full power at the power source 28 is operated or switched off. The switching element 26 is through the activation signal A operated, that is closed or opened. The heating element 12 is therefore indeed on the switching element 26 controlled, but otherwise unregulated or unthrottled at the power source 28 operable or alternatively switched off.

2 symbolically shows the arrangement according to 1 resulting control loop with the first two-step controller 20 and the second two-position controller 22 , Command value in the control loop is the setpoint TWS for the water temperature TW , Controlled variable is the actual value TWI the water temperature TW , The deviation TWS - TWI becomes the first two-position controller 20 led, which with threshold 0 from an output signal 0 on an output signal 1 on. As its control value is thus 0 for TWI greater or equal TWS and 1 for TWI smaller TWS , For values TWI less the limit G the manipulated variable is directly applied to the switching element 26 led (branching 32 in dashed line). For values TWI greater G (and TWI smaller TWS ), the manipulated variable is alternatively the first two-position controller 20 supplied and this with the setpoint THS multiplied as a reference variable for the second two-position controller 22 used. Controlled variable is the actual value there THI , The deviation THS - THI goes to the second two-position controller 22 which is identical to the first two-position controller 20 is executed. Its manipulated variable (zero or one) is then applied to the switching element 26 guided. For values one of the manipulated variable becomes the switching element 26 closed, opened for values zero.

3a shows symbolically over time t different sizes during a heating process for initially cold water 4 in the heater 2 , Plotted are the water temperature actual value TWI (° C), the actual value THI the heating temperature (° C) and the current I as a percentage of a rated current IN (Continuous operation of the heating element 12 at the energy source 28 : 100%).

3a shows the conditions in a comparable arrangement according to 1 and 2 but without the presence of the second two-position controller 22 , It is therefore always only the first two-step controller 20 over the full temperature range up to the setpoint TWS active. It can be seen that both during the first heating process (up to approx. 8s) and during holding operations ( 11 - 13s . 14 - 17s . 18s -...) the temperature of the heating element repeatedly rises up to about 80-85 ° C.

3b shows the same time courses, but for the heater according to the invention 2 according to 1 and 2 , Here, as soon as the water temperature TW the limit G exceeds (4s), the regulation by the second two-position controller 22 one which the temperature TH of the heating element 12 limited to 60 ° C. In this case - not visible in the figure - the heating element current in a comparatively fast clock sequence on and off, which in 3b is indicated by an average current of about 50%. When exceeding the setpoint TWS by the water temperature TW (8s, 12s, 16s) is over the superimposed first two-position controller 20 in each case the power is completely switched off (deactivation of the activation signal A ), this is indicated in the figure by the time ranges "A = 0".

4 shows in direct comparison once again the comparison of the heating element temperature TH for the cases from the 3a, b , The heating element 12 experiences significantly less temperature fluctuations and is not heated to correspondingly high temperature values. Both reduce limescale in the heating element 12 and extends its life.

5 shows a comparable comparison of the respective current waveforms from the 3a, b , Here it can be seen that the invention leads to less oscillation amplitude of the current and thus to a less heavy load on the electrical system of the aircraft 30 leads.

LIST OF REFERENCE NUMBERS

2

heater

4

water

6

container

8th

entrance

10

output

12

heating element

14

Water sensor

16

control

18

Heating sensor

20

Two-position controller (first)

22

Two-position controller (second)

24

level sensor

26

switching element

28

energy

30

plane

32

branch

F

filling state

TW

Water temperature

TH

Heating temperature

TWI

Actual value (water temperature)

TWS

Setpoint (water temperature)

THI

Actual value (heating temperature)

THS

Setpoint (heating temperature)

G

limit

A

activation signal

t

Time

I

electricity

IN

current

Claims (12)

Heater (2) for heating water (4), - with a container (6) for filling with water (4), and - with a heating element (12) in a filling state (F) of the container (6) at least partially is in direct contact with the water (4), and - with a water sensor (14) for determining a water temperature (TW) of the water (4) in the filling state (F), and - with a controller (16) for Operating the heating element (12) in the filling state (F) as a function of the water temperature (TW) determined by the water sensor (14), characterized in that - the heating device (2) a heating sensor (18) for determining a heating -Temperature (TH) of the heating element (12), and - the controller (16) for operating the heating element (12) in the filling state (F) also in dependence of the heating sensor (18) determined heating temperature (TH) formed is, - the controller (16) includes at least one two-step controller (20,22), - the controller (16) has a second two-point controller (22) to R Containing an actual value (THI) of the heating temperature (TH) to a setpoint (THS) out, the only in the event that an actual value (TWI) of the water temperature (TW) is greater than a limit (G), the first two-level controller (20) is subordinate and otherwise inactive, wherein the second two-step controller (22) as a manipulated variable has a binary activation signal (A) for the heating element (12). Heater (2) after Claim 1 , characterized in that the controller (16) contains a two-step controller (20) for controlling an actual value (TWI) of the water temperature (TW) to a target value (TWS) out, the two-step controller (20) as a manipulated variable a binary activation signal (A) for the heating element (12). Heater (2) after Claim 2 , characterized in that the desired value (TWS) of the water temperature (TW) can be predetermined. Heater (2) according to one of the preceding claims, characterized in that the limit value (G) of the water temperature (TW) can be predetermined. Heater (2) according to one of the preceding claims, characterized in that the limit value (G) of the water temperature (TW) is selected depending on the setpoint value (TWS). Heater (2) according to one of the preceding claims, characterized in that the desired value (THS) of the heating temperature (TH) can be predetermined. Heater (2) according to one of the preceding claims, characterized in that the desired value (THS) of the heating temperature (TH) is selected as a function of the desired value (TWS) of the water temperature (TW). Heater (2) according to one of the preceding claims, characterized in that the heater (2) includes a level sensor (24) and the heating element (12) is activated only when the fill level sensor (24) of the filling state (F) is sensed. Heater (2) according to one of the preceding claims, characterized in that the heating element (12) is an electrical resistance heating element. Heater (2) according to one of the preceding claims, characterized in that the Heater (2) is a heater (2) for an aircraft (30). Method for operating a heater (2) according to one of Claims 1 to 10 , characterized in that the controller (16) operates the heating element (12) in dependence on the water temperature (TW) and in dependence on the heating temperature (TH), and the heating element (12) is activated only if the actual value (TWI) of the water temperature (TW) is less than a target value (TWS), and in the case that the actual value (TWI) of the water temperature (TW) is greater than a limit value (G), the heating element (12) only is then activated when an actual value (THI) of the heating temperature (TH) is less than a desired value (THS). Method according to Claim 11 , characterized in that the heating element (12) is activated by being connected unregulated to a power source (28).

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