Electrode-type steam humidifier and its operation method

Abstract

The present invention relates to an electrode-based steam humidifier (1), a method for its operation and a computer program product suitable for carrying out said method, comprising a steam vessel (2) having a first water inlet (10) for mineral water and at least two electrodes (6) arranged to be at least partially immersed in water filled above a minimum water level, the electrodes (6) being supplied with a voltage such that at least one of the electrodes (6) has a different electrical potential than the other electrode or electrodes (6) and generates an electric current in the water, the steam vessel (2) comprising a second water inlet (11) for demineralized water and means for evaluating the electrical conductivity of the water held in the steam vessel (2), the flow rate through both water inlets (10, 11) for refilling the steam vessel (2) being controlled by a controller (20) based on the evaluated electrical conductivity in order to obtain or maintain a desired electrical conductivity. A method of operating an electrode-based steam humidifier (1) includes assessing the conductivity of water in a steam container (2) of the electrode-based steam humidifier (1) and adjusting the conductivity of water introduced into the steam container (2) for refilling such that the resulting water mixture in the steam container (2) has a desired conductivity. A computer program product of the invention includes program portions designed to carry out the invention when loaded into a digital controller connected to at least the necessary sensors and actuators of the electrode-based steam humidifier (1).

Description

[Technical field]

[0001] The present invention relates to an electrode-based steam humidifier and a method of operation thereof, as well as a computer program product suitable for carrying out the method.

[0002] Known electrode steam humidifiers comprise a steam cylinder with electrodes protruding inside. When filled with sufficient tap water and a sufficient voltage is applied to the electrodes, a current flows through the water, eventually boiling the water and generating steam. The drop in water level due to the extracted steam is usually balanced by intermittently refilling tap water to a predefined level once the water level has dropped to a certain level. Apart from the possibility of a maximum fill level sensor limiting the amount of water taken to a predefined level, the water level in the steam cylinder is generally regulated based on the power consumed by the steam generation.

[0003] The steam produced is pure, and the mineral matter originally dissolved in the tap water remains in the steam cylinder, increasing the concentration of mineral elements in the water in the steam cylinder. Dissolved mineral matter is essential for the functioning of electrode steam humidifiers because they provide the necessary electrical conductivity. However, this increased mineral concentration has some significant drawbacks. It leads to increased electrical conductivity of the water, which leads to increased corrosion of the electrodes and increased formation of limescale.

[0004] To counter these drawbacks and ensure the operability of electrode steam humidifiers, the steam cylinder must be drained completely periodically and the saline water replaced with fresh tap water. Precipitated mineral residues must also be removed periodically, for example during drainage treatment or regular maintenance cycles.

[0005] It is an object of the present invention to provide an electrode-based steam humidifier, a method of operating an electrode-based steam humidifier, and a corresponding computer program product that at least alleviates these disadvantages.

[0006] This object is solved by an electrode-based steam humidifier, a method and a computer program product according to the independent claims. Preferred embodiments are subject of the dependent claims.

[0007] The invention thus comprises a steam vessel having a first water inlet for mineralized water, and at least two electrodes arranged to be at least partially immersed in water filled above a minimum water level, the electrodes being supplied with a voltage such that at least one of the electrodes has a different potential than the other electrodes causing a current to flow in the water, the steam vessel comprising a second water inlet for demineralized water, and means for assessing the conductivity of the water held in the steam vessel, the flow rate through both water inlets for refilling the steam vessel being controlled by a controller based on the assessed conductivity in order to obtain or maintain a desired conductivity.

[0008] The present invention further relates to a method of operating an electrode-based steam humidifier comprising assessing the conductivity of water in a steam container of the steam humidifier and adjusting the conductivity of water introduced into said steam container for refilling such that the water mixture in said steam container has a desired conductivity.

[0009] The present invention also relates to a computer program product comprising program portions designed to carry out the method of the present invention when loaded into a digital controller connected to at least the necessary sensors and actuators of an electrode-based steam humidifier.

[0010] Before describing the invention in detail, some definitions of terms used in connection with the present invention are provided.

[0011] If the potentials of the electrodes are not generally and intentionally the same, then the electrodes have "different potentials", which is self-evident when a voltage is applied directly to the electrodes. When an AC or polyphase voltage is applied to the electrodes of an electroded steam humidifier, even if the potentials are briefly the same during a cycle, the electrodes are still considered to be at different potentials because they are at different potentials for most of the cycle.

[0012] The present invention recognises that by selectively replenishing water of different purity, the conductivity of the water held within the electrode steam humidifier can be controlled to some extent, resulting in it being able to operate at higher efficiency over longer operating cycles than prior art electrode steam humidifiers. In particular, by maintaining a predetermined level of mineralisation of the water within the steam reservoir, electrode degradation and mineral precipitation can be significantly reduced, so that the maintenance cycle of an electrode steam humidifier in accordance with the present invention can be significantly extended compared to that typical of the current state of the art.

[0013] To achieve this, the controller controls the inflow of mineral water (such as tap water) and demineralized water such that a desired conductivity of the water held in the steam vessel is obtained or maintained, at least within a certain tolerance, to counter the effects of steam extraction (which generally increases conductivity) and mineral precipitation (which generally decreases conductivity). The overall inflow and mix ratio of the inflows of mineral water and demineralized water are based on the estimated conductivity of the water already present in the steam generator.

[0014] It has been found that by observing the system response to certain changes in system conditions and taking into account certain system constants and, if necessary, certain estimates, the conductivity can already be assessed with a sufficiently high level of accuracy. For this reason, the means for assessing the conductivity of the water held in the steam container preferably comprises an observation module capable of observing various parameters relating to the operation of the electrode-based steam humidifier sufficient to assess said conductivity. The observation module may be integrated into the controller.

[0015] For example, when the steam vessel is filled for the first time, if only mineral water is injected through the first water inlet, or a predetermined mixture of mineral water and demineralized water is injected through both water inlets to a predetermined level, the response of the system to the application of a predetermined voltage to the electrodes can be taken as the desired reference response.

[0016] The response of the system may be observed by measuring the current resulting from applying a given voltage. Over time, the system first exhibits an increase in conductivity, visible as an increase in current as the water heats up to boiling. Then, as the water evaporates, the water level in the steam vessel gradually drops, reducing the surface area of ​​the electrodes submerged in water and causing the current to decrease. If, after the current has reached the lower limit, the steam vessel is refilled with water having the initial conductivity (e.g., using only water from the first inlet or water from both inlets in the mixture ratio originally used), the current will increase again, depending on the temperature of the incoming water, first due to the refill and then due to the temperature rise caused by the current flowing through the water. Of course, depending on the choice of the lower limit, the refilling of water may approximate a continuous water flow.

[0017] As explained, since the change in mineralization of the water in the steam vessel (and therefore the change in conductivity) during the first cycle or first few cycles is negligible, the response of the system during this first cycle or first few cycles may be considered as a baseline response. This baseline response may be stored, for example in digital form, as baseline response data and made accessible to the controller and / or observation module.

[0018] Assuming that relevant environmental and system parameters (e.g., mineral concentrations of the mineral and demineralized water at the first and second inlets and inlet water temperature) are constant, any identifiable deviation from the baseline response during operation would indicate a change in the conductivity of the water in the steam vessel.

[0019] At that point, the mixture ratio of mineral water and demineralized water refilling the steam vessel can be systematically adjusted to bring the overall conductivity of the water in the steam vessel closer to the conductivity on which the reference response is based. The change in the mixture ratio can be defined, for example, by a characteristic curve (e.g. stored in digital form) accessible to the controller and / or observation module, or it can be defined by a mathematical formula. It can also be derived from modeling of the system.

[0020] As outlined above, it is possible to determine the baseline response of each electrode steam humidifier individually in its intended operating environment, but it is of course also possible to provide previously created baseline response data to the controller and / or observation module. The baseline response data for a particular electrode steam humidifier and / or its operating environment may be calculated or selected from an appropriate baseline response data catalog based on specific parameters (e.g. the structural design of the electrode steam humidifier, in particular the number and arrangement of the electrodes, or the mineral concentration of the water provided by the first water inlet).

[0021] Furthermore, the controller and / or observation module may also be equipped with machine learning algorithms that, starting from a predefined characteristic curve for adjusting the mixing ratio of, for example, mineral water and demineralized water over time, determine the most appropriate mixing adjustments in case of deviations from the baseline response.

[0022] As explained, it is possible to control the conductivity of the water in the steam vessel by simply evaluating the system response during operation with sufficient accuracy, but by utilizing additional sensor information, the control of the conductivity can be further enhanced and the reliance on indirectly determined or assumed values ​​can be reduced. The additional sensor information can be sent to the observation module and taken into account when evaluating the current system response compared to the reference response. Potentially, it is also possible to directly collect all relevant parameters for evaluating the conductivity of the water in the steam vessel with suitable sensors. In this case, the observation module is omitted and all measurements are directly processed by the controller.

[0023] The electrode-based steam humidifier may preferably comprise a sensor electrode for indicating that the water level in the steam container is above a predetermined level. For this purpose, the tip of the sensor electrode is located at the predetermined level and the detection value of the sensor depends on whether the tip of the sensor is submerged in water or above the water surface. Such sensor electrodes are generally known in the prior art and are already used, for example, as maximum water level indicators.

[0024] Switching between these two detection states of the sensor electrodes may be interpreted by the controller as a signal that the water level in the steam vessel has reached, is at, or is below a predetermined level. Deviations from the expected baseline response of the system at this particular water level may be interpreted as being caused by other changes to the system, such as a change in the conductivity of the water.

[0025] The sensor electrode is preferably arranged to detect the water level at which the steam container is periodically refilled to compensate for water loss due to steam generation, and may also be used as an indicator to stop the inflow of water from the water inlet without affecting the above function.

[0026] Although the sensor electrode works reliably in most cases, depending on the quality of the water used in the electrode steam humidifier, in particular the quality of the mineral water at the first water inlet, bubbles may form in the steam container under certain circumstances, in particular during refilling or when the water is boiling. Since bubbles can lead to inaccurate readings of the sensor electrode, a water level detector may be provided in addition to or instead of the sensor electrode, which is free from or at least less prone to erroneous readings due to bubbles. In contrast to the sensor electrode, the water level detector is not only able to detect whether the water level is below or above a given level, but also to determine any water level within the measurement range. It may be one or more reed contacts operated by a float in a separate container in communication with the steam, or a capacitive water level sensor, as disclosed for example in DE 20 2016 005 944 U1. In order to avoid or at least reduce any possible interferences, such as for example the formation of bubbles in the water level detector, the detector is arranged in a container separate from the steam container, said containers forming communicating vessels. In such an arrangement, bubble formation when boiling water and other effects that may affect the measurement accuracy of the water level sensor are generally confined to the steam vessel and do not affect a water level sensor installed in a separate vessel.

[0027] In a preferred embodiment, a conductivity sensor may be provided in the steam container or in a container in communication therewith. The sensor is preferably located below a typical water level during normal operation of the electrode-type steam humidifier. The provision of the conductivity sensor eliminates the need to indirectly determine the conductivity by measuring the current generated when a predetermined voltage is applied to the electrodes. Indirect measurements may be more prone to errors than direct measurements of conductivity, such as electrode wear.

[0028] Alternatively or additionally, a conductivity sensor may be provided at one or both of the water inlets and / or at a location where two separate inlets are joined to provide a combined inflow of already mixed water. By locating the conductivity sensor at the inlet, the quality of the mineral water, demineralized water and / or the mixture thereof can be observed and taken into account by the controller. For example, the inflow through both inlets can be adjusted to obtain a desired conductivity of the mixed water.

[0029] Preferably, the electrodes and / or their number are optimized to allow the electrode steam humidifier to achieve the lowest possible water conductivity. Three electrodes are recommended for steam outputs up to 15 kg / h, six electrodes for steam outputs between 20 and 65 kg / h. The surface area of ​​the electrodes as a function of the rated current is preferably between 5 and 30 cm for full-surface electrodes. 2 / A, more preferably 10-20cm 2 / A, and in the case of a mesh electrode, the thickness is preferably 5 to 25 cm 2 / A, more preferably 5-15cm 2 / A, but full-surface electrodes are preferred. The surface distance between two adjacent electrodes having different potentials is preferably 25 to 50 mm for a maximum rated potential difference of 400 V (e.g., generated by AC), 15 to 35 mm for a maximum rated potential difference of 200 V, and 50 to 80 mm for a maximum rated potential difference of 690 V.

[0030] The electrode-based steam humidifier may include a solenoid or motor valve at the first and / or second water inlet that is controllable by the controller, or, if the demineralized water is supplied from an external water treatment device, the electrode-based steam humidifier may include an interface to the external water treatment device connected to the second water inlet for controlling the demineralized water output of the water treatment device.

[0031] As already explained, applying a voltage to the electrodes causes a current to flow in the water, which heats it up and changes its conductivity. The current will also increase until the water boils and a maximum value for steam production is reached. Boiling removes steam, lowering the water level in the steam container and resulting in a decrease in steam production. When the steam container is refilled, the cycle starts anew and steam production increases to a maximum. Typically, in known electrode steam humidifiers, depending on the actual design, the variation in steam production over the entire refill cycle can be up to ±2.5%, or even ±10%, around a given set point preset by the structural configuration of the electrode steam humidifier or by the settings of various process parameters such as voltage, maximum current and / or power.

[0032] To reduce this variability, the controller is preferably configured to provide finer control over the steam production of the electrode-based steam humidifier.

[0033] To this end, the controller may be configured to regulate the power conducted through the electrodes. In particular, the controller may limit or mitigate the increase in current due to an increase in the conductivity of the water in order to regulate the steam generation. This can avoid or at least reduce overshoot in the steam generation when boiling water. Known techniques such as pulse width modulation (PWM), AC / AC conversion, leading-edge cutoff, trailing-edge cutoff, etc. may be used to regulate the power.

[0034] If water level detection is present, the controller may be configured to control steam production based on the water level corresponding to the immersion depth of the electrode. The water level detector allows for more accurate water replenishment and reduces water level fluctuations during operation compared to a sensor electrode. Less water level fluctuation means less fluctuation in steam production.

[0035] For a description of the method according to the invention see generally above.

[0036] In the method of operating the electrode-based steam humidifier of the present invention, the conductivity of the water in the steam container of the steam humidifier is evaluated, and the evaluation may be based on observation, direct measurement, and / or indirect measurement of the system response. The conductivity of the water introduced into the steam container for refilling, which is typically required during operation of the electrode-based steam humidifier, is adjusted so that the resulting mixture of water in the steam container has a desired conductivity. That is, if the conductivity of the water in the steam container is above a desired level, water with a lower conductivity is introduced for refilling, and if it is below the desired level, water with a higher conductivity is introduced for refilling. The conductivity of the water used for refilling may be adjusted by mixing water from two sources having different conductivities.

[0037] Preferably, the assessment of the conductivity of the water in the steam container is based on observing at least one system response during normal operation of the electrode steam humidifier. Observing the system response of the electrode steam humidifier generally allows the method to be applied to existing electrode steam humidifiers and electrode steam humidifier designs without requiring structural modifications. In many cases, only the electrode steam humidifier controller needs to be updated to be able to observe and respond to the system response.

[0038] The method of the present invention is preferably implemented in the electrode steam humidifier of the present invention, but is not limited to this particular embodiment. Rather, the method of the present invention may also be realized with a known electrode steam humidifier having a single water inlet and a water source connected thereto, where the water source is controllable with respect to the mineralization of the water supplied to the electrode steam humidifier. One example of such a water source is an infiltration unit for purifying mineral water, with a controllable bypass for the mineral water.

[0039] Thus, the controller of the electrode steam humidifier can execute the method of the present invention, which can control an external controllable water source via a suitable interface, or preferably, a separate controller can execute the method of the present invention. In this case, said separate controller must be provided with all readings necessary for executing the method and must be configured to control the electrode steam humidifier and all other possible components via a suitable interface. In other words, the controller executing the computer program product of the present invention must be connected to all necessary sensors and actuators of the electrode steam humidifier, as well as all other possible components. [Brief description of the drawings]

[0040] The invention will now be described in more detail with reference to the accompanying drawings, in which:

[0041] [Figure 1] 1 is a schematic diagram of a first exemplary embodiment of an electrode-based steam humidifier according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] 1 shows a schematic diagram of an electrode-type steam humidifier 1 according to the present invention. By describing the electrode-type steam humidifier 1, not only the device of the present invention but also the method of the present invention will become readily apparent.

[0043] The electrode type steam humidifier comprises a steam container 1. The steam container 1 comprises a steam container 2 in the form of a steam cylinder. The steam container 2 comprises an inlet 3 and a drain 4 having a controllable drain pump 4' at its bottom. At the top there is a steam outlet 5 which is connected to other equipment (not shown) which requires steam at least temporarily, for example an air conditioning control unit.

[0044] Six electrodes 6 are arranged in the steam vessel 2 at equal intervals around the circumference. These electrodes 6 are arranged so as to be able to boil water of limited conductivity and therefore have large mutually facing surfaces (in this case about 20 cm2 each). 2 / A). The electrodes 6 are depicted as simple plate electrodes, but may have a more complicated design, for example a V-shape, so that the surfaces of two adjacent electrodes 6 may be kept at a constant distance over the entire area.

[0045] The electrodes 6 are individually electrically connected via connection lines 8 to a power distribution unit 7 which is connected to an external power source, for example a power grid (not shown). The power distribution unit 7 is configured to supply the electrodes with a DC or AC voltage, such that the potential of two adjacent electrodes 6 is different. Furthermore, the power distribution unit 7 provides the functionality of measuring the total current flowing between the electrodes 6 and limiting the current flow (and therefore the power consumed by the electrodes 6 assuming a constant voltage) to an externally supplied set value.

[0046] Via a Y-connector 9, the intake 3 is connected to two separate water inlets 10, 11, the flow rate of which can be controlled in this example by solenoid valves 12, 13. The first water inlet 10 is for mineral water, which is usually tap water, the other water inlet 11 is for demineralised water.

[0047] A conductivity sensor 14 is provided at the connection between the Y-connector 9 and the inlet 3 to measure the conductivity of water passing through the connection.

[0048] In addition, a sensor electrode 15 protruding a predetermined length from the upper portion of the steam container 2 is provided. The sensor electrode 15 detects whether or not its tip is immersed in water.

[0049] In parallel thereto, a water level detector 16 is provided. The water level detector 16, which is connected to the steam vessel 2 via a connecting pipe, is, for example, a capacitive water level sensor as disclosed in DE 20 2016 005 944 U1 and makes it possible to accurately determine the water level in the steam vessel 2 within a range in the vicinity of the water level defined by the sensor electrode 15. This range is determined primarily by the length of the water level detector 16.

[0050] That is, the conductivity sensor 14 capable of measuring the total current, the sensor electrode 15, the water level detector 16 and the power distribution unit 7, as well as all the controllable devices, i.e. the various valves 12 and 13, the drain pump 4' and the power distribution unit 7 for the power limiting function, are connected to a controller 20, which also comprises an observation module 21.

[0051] For operation, the steam vessel 2 is first filled with water of a given conductivity up to a water level defined by the sensor electrode 15 by opening the two solenoid valves 12, 13 of the two water inlets 10, 11. The controller 20 then opens each valve 12, 13 to the extent necessary to achieve a mixture of the desired conductivity. The given conductivity of the water entering during filling is constantly monitored via the conductivity sensor 14. In case of deviation from the desired conductivity, the controller 20 is configured to adjust the valves 12, 13 and thereby adjust the mixture of mineral water and demineralized water to reach the desired conductivity.

[0052] When the sensor electrode 15 and / or water level detector 16 sends a signal to the controller 20 that a predetermined water level has been reached, the valves 12, 13 are closed.

[0053] After the steam vessel 2 is initially filled with water, the electrodes 6 are energized by the power distribution unit 7, causing adjacent electrodes 6 to be at different potentials and generating a current in the water due to the conductivity of the water. The total current is measured by the power distribution unit 7 and reported to the controller 20.

[0054] Passing an electric current through the water causes it to heat up and boil, producing steam which is expelled through the steam outlet 5. During heating, the conductivity of the water increases and is recorded by the power distribution unit 7 and controller 20 due to an increase in the current through the electrodes 6.

[0055] Steam extraction causes a drop in the water level in the steam vessel 2 which is sensed by the sensor electrode 15 and / or the water level detector 16 and typically leads to a drop in the current. The drop in water level is recorded in the controller 20 by the sensor electrode 15 reporting that the water level is below the tip of the electrode in combination with a drop in current by a predetermined amount, or by the water level detector 16, and is typically addressed by refilling the steam vessel 2 with water from the first and / or second water inlets 10, 11.

[0056] Since the generated steam is generally pure, the mineral concentration of the water in the steam vessel 2 will generally increase (albeit slowly) and will also initially contribute to an increase in conductivity. However, increased mineralization can result in precipitation of minerals, which in turn can result in a decrease in the overall conductivity of the water. With the intention of maintaining the conductivity of the water in the steam vessel 2 at a predetermined / initial level, the controller 20 is configured to purposefully adjust the conductivity of the incoming water in order to control the conductivity of the resulting water mixture in the steam vessel 2.

[0057] For this purpose, the controller 20 comprises an observation module 21 configured to evaluate the conductivity of the water in the steam vessel 2 .

[0058] For example, the observation module 21 may observe the maximum current reached each time after the steam container 2 is refilled with water as indicated by the sensor electrode 15. This maximum current is the maximum current reached after heating the water in the steam container 2 to boiling temperature. For example, deviations from the current measured during the initial heating cycle (see above), which may be considered as a baseline response of the system of the electrode-based steam humidifier 1, may be interpreted as deviations in the conductivity of the water in the steam container 2 and can be addressed by the controller 20 by adjusting the mixture of mineral water and demineralized water used for refilling according to a characteristic curve stored in the controller 20.

[0059] Alternatively or additionally, the conductivity of the water in the steam vessel 2 may be derived from the current measured by the power distribution unit 7 and the water level detected by the water level detector 16. These results may be compared to an expected standard system response stored in the controller and any deviations may be interpreted as deviations from the desired conductivity of the water in the steam vessel 2. Again, the controller 20 may address this deviation by adjusting the mixture of mineral water and demineralized water used for refilling according to a characteristic curve stored in the controller 20.

[0060] As the conductivity of the water mixture flowing into the steam vessel 2 is monitored by the conductivity sensor 14, the controller 20 and / or the observation module 21 may apply machine learning algorithms based on the measured conductivity and its assessed impact on the conductivity of the water in the steam vessel 2.

[0061] In either case, based on one or both of the above methods, i.e., the sensor electrode 15 and the water level detector 16, the controller 20 can maintain a generally constant mineral concentration of the water in the steam container 2 during operation of the electrode-based steam humidifier 1.

[0062] For this reason, although the periods between complete changes of the water in the steam canister 2 and other maintenance cycles may be extended, the steam canister 2 should be thoroughly cleaned from time to time to flush out as much of the precipitated mineral build-up as possible. For this reason, the controller 20 may operate the drain pump 4' to pump water from the steam canister 2 through the drain outlet 4. Once the steam canister 2 is emptied, the drain pump 4' is stopped and the steam canister 2 is refilled with water as previously described.

[0063] The electrode-based steam humidifier 1 shown in FIG. 1 may provide additional advantages.

[0064] By using the disclosed techniques of assessing the water level, or at least assessing that a predetermined water level has been reached, i.e., both via the sensor electrode 15 and the water level detector 16, the formation of bubbles in the steam container 2 can be detected because bubbles in the steam container 2 trigger the sensor electrode 15 before the actual water level detectable by the water level detector 16, which is usually not affected by bubble formation in the steam container 2, reaches the tip of the sensor electrode 15. The formation of bubbles in the steam container 2 may indicate impurities or poor water quality in the water (which is usually mineral water, which is tap water), and may require more frequent maintenance and / or cleaning of the electrode type steam humidifier 1, particularly the steam container 2 and the electrode 6, to ensure long-term operation of the electrode type steam humidifier 1.

[0065] To reduce variability in steam production, the controller 20 may be configured to mitigate increases in power conducted through the electrodes 6 by sending appropriate control commands to the power distribution unit 7 to keep the water level in the steam container 2 as close as possible to a desired water level, for example as defined by the sensor electrode 15, using the water level detector 16. Both measures help to keep the steam production of the electrode based steam humidifier 1 more consistent.

Claims

1. a steam vessel (2) having a first water inlet (10) for mineral water; At least two electrodes (6) arranged so that at least a portion of the electrodes is immersed in water that is filled to a minimum water level or higher; A voltage is applied to the electrodes (6) such that at least one of the electrodes (6) has a different potential from the other electrodes (6) to generate a current in the water; The steam vessel (2) comprises: a second water inlet (11) for desalinated water; and a means for evaluating the electrical conductivity of the water held in the steam vessel (2), 1. An electrode-type steam humidifier (1), characterized in that the flow rate through both water inlets (10, 11) for refilling the steam container (2) is controlled by a controller (20) based on the evaluated conductivity to obtain or maintain a desired conductivity.

2. 2. The electrode-type steam humidifier of claim 1, wherein the means for evaluating the conductivity of the water held in the steam container (2) comprises an observation module (21) capable of observing at least one operating parameter of the electrode-type steam humidifier (1) sufficient to evaluate the conductivity.

3. 3. The electrode steam humidifier of claim 2, wherein the at least one operating parameter comprises a current through the electrode (6).

4. 4. An electrode-type steam humidifier as claimed in claim 1, further comprising a sensor electrode (15) for indicating that the water level in the steam container (2) is above a predetermined level.

5. 5. An electrode-type steam humidifier as claimed in any one of claims 1 to 4, further comprising a water level detector (16), preferably arranged in a container separate from the steam container (2), the containers forming a communicating container.

6. 6. An electrode-type steam humidifier as claimed in any one of claims 1 to 5, wherein at least one conductivity sensor (14) is provided in the steam container (2), in a container in communication with the steam container (2), in one or both of the water inlets (10, 11), and / or at a location where two separate inlets (10, 11) are combined to provide a combined inflow of already mixed water into the steam container (2).

7. The surface area of ​​each electrode (6) as a function of the rated current is 5 to 30 cm for a full surface electrode. ２ / A, preferably 10 to 20 cm ２ / A, 5 to 25 cm for mesh electrodes ２ / A, more preferably 5 to 15 cm ２ / A, and / or the surface distance between two adjacent electrodes (6) having different potentials is 25 to 50 mm when the maximum rated potential difference is 400 V, 15 to 35 mm when the maximum rated potential difference is 200 V, and 50 to 80 mm when the maximum rated potential difference is 690 V.

8. 8. An electrode-type steam humidifier as described in any one of claims 1 to 7, wherein the first water inlet and / or the second water inlet (10, 11) is provided with an electromagnetic valve (12, 13) controllable by the controller (20).

9. 9. The electrode-type steam humidifier according to claim 1, wherein the electrode-type steam humidifier (1) is provided with an interface to an external water treatment device connected to the second water inlet (11) for controlling the desalinated water output of the water treatment device.

10. 10. The electrode-type steam humidifier according to claim 1, wherein the steam container (2) is a steam cylinder.

11. 11. An electrode-type steam humidifier as claimed in any one of claims 1 to 10, wherein the controller (20) is configured to adjust the power conducted through the electrodes (6), preferably to limit or mitigate an increase in current due to an increase in the conductivity of the water in the steam container (2).

12. 12. An electrode-type steam humidifier as claimed in any one of claims 5 to 11, wherein the controller (20) is configured to control the first and second water inlets (11) depending on the water level detector (16) so as to keep the water level in the steam container (2) constant during operation.

13. The electrical conductivity of the water in the steam container (2) of the electrode-type steam humidifier (1) is evaluated; A method of operating an electrode-type steam humidifier (1) comprising adjusting the conductivity of water introduced into the steam container (2) for refilling such that the water mixture in the steam container (2) has a desired conductivity.

14. 14. The method of claim 13, wherein the assessment of the conductivity of the water in the steam container (2) is based on observation of at least one system response during normal operation of the electrode-based steam humidifier.

15. A computer program product comprising program portions designed to carry out the method according to claim 13 or 14 when loaded into a digital controller connected to at least the necessary sensors and actuators of an electrode-based steam humidifier (1).

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