EP2476963B1 - Method for filling and refilling water in a water circuit - Google Patents

Description

Background of the invention

The invention relates to a method for filling and refilling of water in a water circuit, which is supplied by a water supply system with water, in particular in a heating or cooling circuit, wherein between the water cycle and the water supply system, a shut-off valve is arranged by the water in the open state can enter the water cycle, wherein by means of a pressure sensor, the pressure in the water cycle is measured, wherein the shut-off valve is controlled in response to the pressure prevailing in the water cycle pressure such that the shut-off valve opens when the pressure in the water cycle falls below a first limit and that the shut-off valve closes when the pressure exceeds a second threshold, the second threshold being greater than the first threshold.

A valve system for filling or refilling heating systems is, for example, from DE 10 2005 006 790 B4 known. DE 10 2005 006 790 B4 discloses a valve assembly with a ball valve. A pressure sensor controls a servomotor, by which the ball valve is turned into a closed position upon reaching a predetermined system pressure. When the system pressure falls below a predetermined value, the valve ball is rotated back into an open valve position by the servomotor.

DE 102 01 752 B4 discloses a heating system with a make-up valve, via which a Heizwasserkreislauf fresh water can be supplied to keep the pressure in the heating circuit to a predetermined value. If the pressure in the heating water circuit drops, a make-up valve opens and fresh water flows into the heating water circuit. At a given pressure in the heating water circuit, the connection to the fresh water network is interrupted.

As well in DE 10 2005 006 790 B4 as well as in DE 102 01 752 B4 the shut-off or make-up valves are controlled exclusively via the pressure in the heating water circuit. The problem with such valves is that, for example, during a nighttime lowering, night shutdown or at a weather-induced temperature reduction is replenished too much water, because the pressure in the heating circuit at the lowered temperature is low. At a later increase in temperature can then create an overpressure in the heating circuit. Sensitive system components can be damaged. To prevent this, the water must be drained via a pressure relief valve. On the other hand, a too low filling and refilling amount at a certain temperature in the heating circuit can cause the pressure to drop so much in the event of a further temperature reduction that a negative pressure arises in the heating circuit. If there is a negative pressure in the heating circuit, there is a risk that air and thus oxygen will get into the circulation, thus supporting corrosion processes. In addition, it can lead to disturbances of Umwälzbetriebs.

GB 2 377 745 A discloses a method according to the preamble of claim 1 and a system for replenishing water from a secondary system in a heating system, wherein a plurality of system parameters are used to control the system but the pressure limits for controlling the shut-off valve (make-up valve) are kept constant.

In DE 202006016581 U1 is a pressure and temperature controlled safety valve for the protection of domestic water heaters disclosed. The valve opens on the one hand, On the other hand, the valve is controlled by a temperature sensor located in the inlet, which expands as the temperature increases and also opens the valve disk against the preload of the spring. Both control criteria, pressure and temperature, are triggered independently of each other and are determined by the spring force.

Object of the invention

It is an object of the present invention to provide a method for filling and refilling of water in a water cycle, in particular a heating or cooling circuit to be presented in which both damage to the equipment parts are avoided by pressure increase and corrosion due to a negative pressure in the water cycle.

Brief description of the invention

This object is achieved in that a current water temperature of the water in the water cycle detected by a first temperature sensor and transmitted to a control unit, and that the limits for the pressure depending on the determined water temperature are set.

In the method according to the invention, the first and second limit values are not set once but as a function of the measured water temperature. This consideration of the water temperature, the water cycle can be operated with the optimum capacity and under optimal pressure conditions, which ensures energy-saving operation. An overpressure or underpressure after heating up or cooling down eg in the context of a night reduction or night shutdown and the consequences (damage of sensitive parts of the plant in case of overpressure, disturbances in the Circulation, entry of air or oxygen into the water cycle associated with noise and corrosion at low pressure) can thus be avoided.

The first limit value p _GW1 is preferably selected in the range between 0.5 and 1.5 bar, in particular between 1 and 1.5 bar. The second limit value p _GW2 is preferably between 1.5 and 4 bar, in particular between 2 and 3 bar, the difference between the two limit values preferably having a value between 0.05 and 1.5 bar, in particular between 0.2 and 0.5 bar has.

The limits are preferably chosen as a function of the height of the building in which the water cycle is to be operated. The higher the building, the larger the limits are.

"Specification" of the limits means that in the memory of the control unit, an assignment of a respective first limit value p _GW1 and a second limit value p _GW2 to different water temperatures or temperature _{ranges is} stored, for example in the form of a characteristic or a function term.

The determination of the first limit value p _GW1 can be _effected , for example, by establishing a minimum pressure p _min which must not be exceeded in the water cycle (for example, in order to avoid the entry of air). Furthermore, a minimum temperature T _min , which does not fall below the water in the water cycle, determined (eg due to an anti-freeze setting in the water cycle). The first limit value at the minimum temperature is thus greater than the minimum pressure, but preferably only slightly larger, for example of the order of a few tenths bar above the minimum pressure, (p _GW1 (T _min )> ≈ p _min ). Starting from this first limit value p _GW1 (T _min) at minimum temperature of the first limit value p _GW1 (T1) for any current temperature T1 (T1> T _min) is preferably set so that the pressure p, at an assumed temperature reduction from the current water temperature T1 on the minimum temperature T _min the minimum pressure p _min is not below. The behavior of the pressure at temperature change is known or can be determined easily.

The determination of the second limit value p _GW2 can be _effected , for example, by determining a desired operating pressure p _B , which is in the water cycle should not be exceeded. If a safety valve is present, the operating pressure should be less than the opening pressure of the safety valve. In addition, a desired operating temperature T _{B of} the water in the water cycle is determined at which the operating pressure p _{B is to be} achieved. That is, the second limit value p _GW2 (T _B ) at operating temperature T _B is the desired operating pressure (p _GW2 (T _B ) = p _B ). If the water temperature T1 falls below the operating temperature T _B (eg due to a night reduction), the current pressure in the water circuit also drops. The second limit value p _GW2 (T1) for any current temperature T1 (T1 <T _B ) is preferably set so that the operating pressure p _{B is} not exceeded in the event of an assumed temperature increase of the water quantity in the water cycle to the operating temperature T _B. The second limit value p _GW2 for the pressure is therefore dependent in the present case on the current water temperature T1 and the operating temperature T _B at which the water cycle is to be operated. The values for the operating temperature and the associated desired operating pressure can be, for example, empirical values or based on a manufacturer's specification (eg for a particularly economical or component-friendly operation of the water cycle). Based on the manufacturer's specifications or empirical values, characteristic curves, such as in Fig. 1 shown, the limits p _GW1 and p _{GW2 are} determined.

The operating temperature T _{B of} the water in the water cycle can either be determined or determined as a function of another measured variable, eg the outside temperature (as explained in more detail below). The operating temperature T _B is then dependent on this additionally measured size. The limit values depend on the current water temperature T1 and the additionally measured size.

By the limits p _GW1 and p _GW2 so a minimum and maximum amount of water is set, which may be included for the operation of the water cycle with an operating temperature T _B in the water cycle. Does the water circuit contain an expansion tank (eg a membrane expansion tank) as a buffer tank, Dessert of water in the water cycle takes place only when the capacity of the expansion vessel is exhausted.

Advantageous variants of the invention

Preferably, the limits of the pressure p _GW1 and p _GW2 are set so that they decrease with decreasing water temperature T1. The assignment p _GW1 (T1) or p _GW2 (T1) of the limit values for the water temperature is monotonically increasing, in particular strictly monotonically increasing. This avoids that in cooling phases (night reduction, night shutdown, weather-induced reduction) with decreasing pressure p too much water is refilled and at a later increase in the temperature T1 in the regular heating operation creates an overpressure.

A preferred variant of the method according to the invention provides that the shut-off valve opens only when in addition the condition is met that the water temperature exceeds a threshold T _GW . The shut-off valve does not open when the water temperature is less than or equal to the threshold T _GW . In this way, refilling can be completely dispensed with if the water temperature T1 falls below a certain value. This is particularly relevant at times outside the heating season, at a night shutdown or even in case of malfunction of the heating system.

Preferably, the water temperature of the water in the water cycle is detected at several points in the water cycle. This takes into account the fact that the water temperature is usually location-dependent. This is thus taken into account in the temperature dependence of the limits. Thus, for example, an average value of the detected temperatures can be used for the approximate determination of the two limit values p _GW1 and p _GW2 for the pressure in the water cycle. However, it should be taken into account that the real temperatures in the water cycle are sometimes higher or lower. The determination of the limit values p _GW1 and p _GW2 should therefore be correspondingly conservative. Another possibility is to determine the first limit value p _GW1 on the basis of the lowest and the second limit value p _GW2 on the basis of the highest detected temperature.

Preferably, a flow temperature in the flow to a heat consumer and a return temperature in the return are detected by the heat consumer, since there the temperature differences are greatest. Thus, the entire temperature interval in the water cycle is taken into account.

In a particular variant of the method according to the invention, the shut-off valve opens only when in addition the condition is met that the difference between flow temperature T1 _VL and return temperature T1 _RL exceeds a limit .DELTA.T _GW . The limit value of the temperature difference ΔT _GW is dependent on the flow temperature T1 _VL , which influences the pressure p in the water cycle. In this process variant, no filling or refilling takes place when ΔT _GW is exceeded, ie when the heat output is too low, for example, outside the heating period, at a night shutdown or even in a malfunction of the heating system.

A particularly preferred variant of the method _{according to} the invention provides that an outside temperature outside the water cycle is detected by means of a second temperature sensor, and that the limit values p _GW1 and p _{GW2 are set} as a function of the detected outside temperature. The measured outside temperature is the temperature outside the building in which the water circuit is located. The flow temperature T1 is _VL (i.e. of the outside temperature) generally determined depending on the weather. Thus, the pressure p is dependent on the outside temperature. As the outside temperature increases, the flow temperature T1 _VL and thus the pressure p of the water cycle decreases. In the variant according to the invention, the operating temperature T _{B of} the water is regulated / determined as a function of the detected outside temperature T2. This dependence of the operating temperature T _{B of} the water on the outside temperature T2 is included in the determination of the limits.

It may also be advantageous to set the limits p _GW1 and p _GW2 as a function of time. For example, the limits may be day / night-dependent or season-dependent.

Preferably, a system separator separates the water loop from the water supply system when the pressure p of the water loop exceeds the pressure in the water supply system. This prevents that heating water flows back into the drinking water system and the standard DIN EN 1717 is not complied with.

Particularly advantageous is a variant of the method according to the invention in which the shut-off valve closes when the pressure of the water cycle does not increase when water is added to the water cycle. Likewise, the shut-off valve should close when, after a refill, the pressure drops again within a short time. If the pressure does not increase during refilling or if it falls off after refilling within a short time, this indicates a leak. An accidental leakage of water due to such leakage is prevented by closing the shut-off valve.

Preferably, the amount of water in the. Filled or refilled, detected, e.g. by means of a flow meter. By determining the amount of water filled and replenished in the water cycle, unusual quantities can be detected. In addition, in the case of a treatment of the filling water, the amount of water treated can be detected and, if necessary, an exhaustion of a water treatment element can be detected (as explained in more detail below). The value of the measured amount of water is transmitted to the control unit, which according to the data controls the shut-off valve and / or the regeneration of the water treatment element accordingly.

Another indication of leakage is the replenishment of unusually high volumes of water. It is therefore advantageous that the shut-off valve closes when the amount of water filled or replenished in the water cycle exceeds a limit value V _GW . So if exceptional quantities are detected, which indicate a defect or leakage in the heating circuit, the water supply is interrupted. Preferably, a time interval is set within which the limit must be reached for the shut-off valve to close. Instead of a fixed time interval can also be specified that a closing the shut-off valve occurs when the limit is reached during a valve opening (which can vary over time).

In a special variant of the method according to the invention, the conductivity of the water which is filled or refilled into the water cycle is determined. Thus, the quality of the filling water is detected. The quality of the filling water is crucial for a trouble-free and energy-optimized operation of a heating system.

A development of this variant provides that the water is filtered and / or treated during filling and refilling in the water cycle, preferably in accordance with VDI Guideline 2035. This damage and energy losses are prevented by corrosion and stone formation.

For example, water treatment may include desalting and / or softening (replacement of calcium and magnesium ions with sodium ions). In the case of desalination, increasing the conductivity of the treated water indicates a depletion of the water treatment unit; softening reduces the conductivity of the treated water in the event of exhaustion. Therefore, in order to monitor the exhaustion state of a water treatment unit, it is preferable that the measurement of the conductivity of the water after treatment of the water is performed, and the shut-off valve closes when the difference between the measured conductivity of the treated water and a target conductivity value exceeds a threshold indicating a depletion of the water treatment unit. Thus, the state of exhaustion can be monitored. The nominal conductivity value is stored in the control unit.

The invention also relates to a device for carrying out the method according to the invention, in particular a heating filling station, comprising: a temperature sensor for measuring the water temperature in the water cycle; a shut-off valve, which is arranged between the water circuit and a water supply system, a pressure sensor for measuring the pressure in the water cycle, means for transmitting the measured temperature and Pressure values to a control unit for controlling the shut-off valve in dependence on the measured pressure in the water circuit and the measured water temperature, wherein the control unit has a memory in which the following values are stored: a first limit of the pressure prevailing in the water cycle as a function of the measured temperature and a second limit of the pressure prevailing in the water cycle as a function of the measured temperature, wherein the second limit value is greater than the first limit value.

The temperature sensor of the device according to the invention can also be a temperature sensor already present in the water cycle, which is connected to the control unit for the purpose of transmitting the measured temperature values.

Preferably, a second temperature sensor is provided for measuring an outside temperature outside the water cycle, so that the limit values can be determined as a function of the outside temperature (as described above).

Further advantageous embodiments of the device according to the invention may comprise the following components alone or in combination with each other: other temperature sensors for measuring the water temperature at different points of the water cycle; System separator for separating the water cycle from the water supply system; Water meter for measuring the amount of water that is filled in the water cycle or refilled; Water treatment unit for treating (e.g., filtering, desalinating, softening) the water that is being replenished into the water loop; and conductivity meter for measuring the conductivity of the treated or untreated water, which is filled in the water cycle or refilled.

Further advantages of the invention will become apparent from the description and the drawings. Likewise, the features mentioned above and those listed further may be used individually or in any combination Find. The embodiments shown and described are not to be understood as exhaustive enumeration, but rather have exemplary character for the description of the invention.

Drawing and detailed description of the invention

Fig. 1

eine grafische Darstellung des Füllvolumens eines Wasserkreislaufes und des Drucks im Heizkreislauf (Wassermenge im Wasserkreislauf) in Abhängigkeit von der Wassertemperatur des Wassers im Wasserkreislauf;

Fig. 2

eine grafische Darstellung der Abhängigkeit der Vorlauftemperatur und der Rücklauftemperatur von der Außentemperatur (Heizkurve); und

Fig. 3

eine schematische Darstellung eines Heizkreislaufs mit Zuflussleitung für Füll- und Nachfüllwasser mit Mitteln zur Durchführung des erfindungsgemäßen Verfahrens.

Show it:

Fig. 1

a graphic representation of the filling volume of a water cycle and the pressure in the heating circuit (amount of water in the water cycle) as a function of the water temperature of the water in the water cycle;

Fig. 2

a graphic representation of the dependence of the flow temperature and the return temperature of the outside temperature (heating curve); and

Fig. 3

a schematic representation of a heating circuit with inlet line for filling and refilling water with means for carrying out the method according to the invention.

Fig. 1 shows by way of example the volume of the filling water in a heating circuit as a function of the temperature of the filling water (water temperature T1). The filling volume here is 200 l at 20 ° C. As the temperature increases, the density of the water decreases. The specific volume as reciprocal of the density increases accordingly. At 70 ° C, the volume of filling water has expanded to about 204 liters. The increase in pressure due to this volume increase in a closed heating circuit with a membrane expansion vessel 6 is in Fig. 1 Approximated (dashed line). The pressure p rises from 1.2 bar at 20 ° C to about 1.7 bar at 70 ° C. This situation occurs, for example, when the water in the water cycle is brought back to operating temperature after a night setback. At this point it should be emphasized that the volume and pressure increase described only by the temperature increase, but not by a Refill process is conditional. This must be taken into account during filling and refilling operations, which involve an additional pressure change.

It is customary to set the flow temperature T1 _VL (temperature of the filling water before passing through a heat consumer) of a heating water circuit in dependence on the outside temperature T2. Fig. 2 Ideally shows an allocation of the flow temperature T1 _VL to the outside temperature T2, the so-called heating curve or heating curve. The exact course of the heating curve is set for the plant and building. Generally, however, the colder it gets, the more heat is needed. This corresponds to a higher flow temperature T1 _VL . The resulting from the heat output of the radiator return temperature T1 _RL as a function of the outside temperature T2 is in Fig. 2 also shown graphically. If the outside temperature T2 exceeds the heating limit, a controller switches off the heating system (here at + 15 ° C).

As in Fig. 1 1, the pressure p in the heating circuit depends on the temperature T1 and, as just described, on the outside temperature T2. In filling and Nachfüllprozessen according to the inventive method, this is taken into account by the temperatures T1 and T2 are determined and the limits of the pressure p _GW1 or p _GW2 for controlling the shut-off valve are dependent on the detected temperatures T1 and T2.

Fig. 3 shows a Heizungsfüllstation 1 for performing the method according to the invention, which is connected to a water circuit 2, here a heating circuit of a heating system of a building. In the water cycle 2, a circulating pump 3, a plurality of radiators 4a, 4b, a boiler 5 and a diaphragm expansion vessel 6 are provided.

Via an inlet 7 of the heating filling station 1 flows to water, such as from the local drinking water network. At the inlet 7, the water flow can be blocked with a main stopcock 8 . The water passes through a system separator 9 type BA, which prevents backflow of water from the heating circuit 2 in the drinking water network at zulaufseitigem negative pressure. A subsequent pressure reducer 10 ensures a constant operating pressure and protects the heating circuit 2 against overpressure during loading and refilling. The subsequent shut-off valve 11 is motor-actuated by an electronic control unit 12 , here by way of example by means of a servomotor 13th

To control the shut-off valve 11 and thus the amount of water flowing into the heating circuit 2, the pressure p of the heating circuit 2 is detected by means of a pressure sensor 14 which is in communication with the downstream heating circuit 2. Furthermore, the current water temperature T1 of the water in the heating circuit 2 by means of a first temperature sensor 15 and the outside temperature T2 by means of a second temperature sensor 16 are determined. The pressure p and the two temperatures T1 and T2 are transmitted to the electronic control unit 12. In the control unit 12, temperature-dependent pressure limit values p _GW1 and p _{GW2 are stored} in a memory 17 , the shut-off valve 11 opens when the pressure p _falls below the first limit value p _GW1 , and closes when the pressure p exceeds the second limit value p _GW2 , As a result, the pressure p and the amount of water in the heating circuit 2 at each temperature in a favorable for optimal operation of the heating circuit 2 range. A characteristic curve for determining the limit values p _GW1 and p _GW2 can be input to the control unit 12 system-specifically via an input device 18 and displayed by means of a display 19 .

The incoming water is also passed through a water meter 20 , the measurement result (amount of water M) is also passed to the electronic control unit 12. Exceeds the filled or refilled in the heating circuit 2 amount of water M a dependent on the volume of the heating circuit 2 limit or the pressure p does not increase during the filling, this indicates a leak or a defect in the heating circuit 2 out. The shut-off valve 11 interrupts the water supply in this case.

To protect against corrosion and scale formation in the heating circuit 2, the water is treated before entering the heating circuit 2 by means of a water treatment unit 21 (softening, desalination and / or filtration). The shut-off valve 11 can interrupt the flow of water and thus the filling or refilling process even when the water treatment unit 21 is exhausted. For this purpose, the electronic determines Control unit 12 from the treated amount of water M and from the measured with a conductivity sensor 22 conductivity of the untreated water, a residual capacity of the water treatment unit 21. The exhaustion of the water treatment unit 21 may also be signaled by a second conductivity sensor 23 , which monitors the quality of the treated water.

In the method according to the invention, the limits for the pressure in the water cycle at which the water supply to the water cycle is started or interrupted, depending on the water temperature set. This takes into account the dependence of the pressure on the water temperature. The shut-off valve of the arrangement according to the invention opens in contrast to DE 202006016581 U1 not on admission of the valve with a (by pressure or temperature) induced force, which is determined by the design of the valve once, but the shut-off valve is controlled according to the invention by a control unit, which takes into account the associated with a temperature change pressure change in the determination of the limits. The limit values for a certain water temperature can be selected so that even in case of a temperature change, previously definable minimum and maximum values for the pressure of the water cycle are not exceeded or fallen below.

LIST OF REFERENCE NUMBERS

1

Heizungsfüllstation

2

Water cycle (here: heating cycle)

3

circulating pump

4a, 4b

Heat consumer (here: radiator)

5

boiler

6

Diaphragm expansion vessel

7

Intake

8th

main stopcock

9

System separator (e.g., type BA pipe separator)

10

pressure reducer

11

Shut-off valve

12

electronic control unit

13

servomotor

14

pressure sensor

15

Temperature sensor for measuring the water temperature T1 in the water cycle

16

Temperature sensor for measuring the outside temperature T2

17

Memory in which the limits p _GW1 and p _GW2 for the pressure in the water cycle are stored

18

input device

20

water meter

21

Water treatment unit

22

first conductivity sensor for measuring the conductivity of the untreated water

23

second conductivity sensor for measuring the conductivity of the treated water

Claims (17)

1. Method for filling and refilling water into a water circuit (2), in particular, into a heating or cooling circuit, which is supplied with water from a water supply system,
   wherein a stop valve (11) is arranged between the water circuit (2) and the water supply system, through which stop valve in its open state water can enter the water circuit (2),
   wherein the pressure (p) in the water circuit is measured by means of a pressure sensor (14),
   wherein the stop valve (11) is controlled in dependence on the pressure (p) that prevails in the water circuit (2) such that the stop valve (11) opens when the pressure (p) in the water circuit (2) falls below a first limit value (p_GW1) and that the stop valve (11) closes when the pressure (p) exceeds a second limit value (p_GW2), wherein the second limit value (p_GW2) is larger than the first limit value (P_GW1),
   characterized in that
   an instantaneous water temperature (T1, T1_VL, T1_RL) of the water in the water circuit (2) is detected by means of a first temperature sensor (15) and is transferred to a control unit (12), and that the limit values (p_GW1, p_GW2) for the pressure (p) are set in dependence on the detected water temperature (T1, T1_VL , T1_RL).
2. Method according to claim 1, characterized in that the limit values (p_GW1, p_GW2) for the pressure (p) decrease with decreasing water temperature (T1, T1_VL, T1_RL).
3. Method according to any one of the preceding claims, characterized in that the stop valve (11) opens only if the condition is additionally met that the water temperature (T1, T1_VL, T1_RL) exceeds a limit value T_GW.
4. Method according to any one of the preceding claims, characterized in that the water temperature (T1_VL, T1_RL) of the water in the water circuit (2) is detected at a plurality of locations in the water circuit (2).
5. Method according to claim 4, characterized in that a supply temperature (T1_VL) is detected in the supply pipe towards a heat consumer (4a, 4b) and a return temperature (T1_RL) is detected in the return pipe of the heat consumer (4a, 4b).
6. Method according to claim 5, characterized in that the stop valve (11) opens only if the condition is additionally met that the difference between the supply temperature (T1_VL) and the return temperature (T1_RL) exceeds a limit value ΔT_GW.
7. Method according to any one of the preceding claims, characterized in that an outside temperature (T2) outside of the water circuit (2) is detected by means of a second temperature sensor (16) and that the limit values (p_GW1, p_GW2) are set as a function of the detected outside temperature (T2).
8. Method according to any one of the preceding claims, characterized in that the limit values (p_GW1, p_GW2) are defined as a function of time.
9. Method according to any one of the preceding claims, characterized in that a system separator (9) separates the water circuit from the water supply system if the pressure (p) in the water circuit (2) exceeds the pressure in the water supply system.
10. Method according to any one of the preceding claims, characterized in that the stop valve (11) closes if during refilling of water into the water circuit (2) the pressure (p) does not increase.
11. Method according to any one of the preceding claims, characterized in that the amount of water is detected, which is filled or refilled into the water circuit (2).
12. Method according to claim 11, characterized in that the stop valve (11) closes if the amount of water that is filled or refilled into the water circuit (2) exceeds a limit value V_GW.
13. Method according to any one of the preceding claims, characterized in that the conductivity of the water which is filled or refilled into the water circuit (2) is determined.
14. Method according to claim 13, characterized in that the water is filtered and/or treated during filling or refilling into the water circuit (2).
15. Method according to claim 14, characterized in that the measurement of the conductivity of the water is performed after treatment of the water, and that
    the stop valve (11) closes if the difference between the measured conductivity of the treated water and a desired conductivity value exceeds a limit value which indicates depletion of a water treatment unit (21).
16. Device for performing the method according to any one of the preceding claims, comprising:

    a temperature sensor (15) for measuring the water temperature in the water circuit (2),

    a stop valve (11) which is arranged between the water circuit (2) and a water supply system,

    a pressure sensor (14) for measuring the pressure (p) in the water circuit (2),

    means for transmitting the measured temperature values and pressure values to a control unit (12) for controlling the stop valve (11) in dependence on the measured pressure (p) in the water circuit (2) and the measured water temperature (T1, T1_VL, T1_RL), wherein the control unlit (12) has a storage in which the following values are stored:

    a first limit value (p_GW1) of the pressure (p) that prevails in the water circuit (2) in dependence on the measured temperature (T1, T1_VL, T1_RL),

    a second limit value (p_GW2) of the pressure (p) that prevails in the water circuit (2) in dependence on the measured temperature (T1, T1_VL, T1_RL),

    wherein the second limit value (p_GW2) is larger than the first limit value (p_GW1).
17. Device according to claim 16, characterized in that a second temperature sensor (16) is provided for measuring an outside temperature (T2) outside of the water circuit (2).

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