Instantaneous electric water heater and control method thereof

Abstract

The present invention provides an instant electric water heater and a control method thereof. The instant electric water heater includes a cold water inlet passage, a hot water outlet passage, and a water heating zone disposed between the inlet passage and the outlet passage, which together form a water flow passage through which water flows. The electric water heater also includes a heating element located in the water heating zone, a sensor for measuring the temperature of the hot water, a controller, and a measuring device. The measuring device is connected to the controller and to first and second measuring electrodes through two wires. The two wires are connected in parallel to a resistor to eliminate electromagnetic interference from the heating element. The measuring device is designed to continuously measure the instantaneous resistance between the two wires using alternating current. By providing a device for continuously measuring the water conductivity and preventing electric shock due to water contamination, the device is low in cost because it uses general equipment components and a simple measuring circuit.

Description

Technical Field

[0001] This invention relates to an electric water heater, and more particularly to an instantaneous electric water heater that heats water by immersing a heating element in water, and is equipped with a device for continuously measuring the conductivity of water.

[0002] The present invention also relates to a method for controlling the above-mentioned instantaneous electric water heater. Background Technology

[0003] In the prior art, known heating equipment, especially hot water boilers, includes a water heating source (gas, electricity, solar energy, heat pump system), a water circulation pump, and one or more heating circuits.

[0004] Electric water heaters are typically used to prepare hot water for households that use electricity or other inhabited buildings.

[0005] This type of electric water heater includes one or more electric heating elements that heat water flowing through the water flow channels of the water heater to a desired temperature. The electric water heater heats water on demand, and the heated water does not accumulate in the water heater. Electric water heaters are typically equipped with bare wire heating elements, forming a heating coil.

[0006] The potential difference between the bare wire and the water supply or drainage channel electrically connected to ground causes a corresponding current leakage during the operation of the heating device. The extent of this current leakage depends on factors such as the conductivity of the water flowing through the equipment.

[0007] Several standards apply to household electric water heaters, among which safe operation is the most important. Failure to comply with these regulations may result in electric shock.

[0008] International standard DIN EN 60335-2-21 relates to the safety of domestic storage-type electric water heaters, with section 13.2 specifying the maximum leakage current value for domestic electrical equipment; standard DIN EN 60335-2-35 relates to the safety of instantaneous electric water heaters, with a table in section 7.1 containing limits on the conductivity of water at operating temperatures.

[0009] Because water in distribution networks is frequently contaminated with salt or other unwanted impurities in different parts of the world, leading to increased water conductivity, it is necessary to continuously assess the water conductivity during the operation of instantaneous electric water heaters to meet safety standards. If the conductivity exceeds the limit, all necessary steps must be taken, such as disconnecting the heater from the power supply.

[0010] In the prior art, solutions for measuring water resistance or water conductivity are known. Publication DE8428975 U1 discloses an instantaneous electric water heater with a method for measuring water conductivity and assessing, for example, water shortage caused by air bubbles, based on this value, wherein measuring electrodes are screwed into the water channel. According to this measurement, the current supply to the heating coil is only turned on when the conductivity measurement indicates sufficient water in the water flow channel of the water heater. Once a leak is detected, the heating coil can be immediately shut off during operation. The above solution does not consider the water conductivity limits specified by standards and cannot guarantee the safety of equipment operation.

[0011] Publication EP 2840404 B1 discloses a method for controlling a bare-wire instantaneous electric water heater. The instantaneous electric water heater includes a control device comprising an evaluation unit configured to determine an assumed value for current leakage based on a water conductivity value and at least one predetermined value related to the device's construction (design). The control device is adapted to reduce the heating power of the bare-wire heating element when the assumed value for current leakage exceeds a predetermined threshold for current leakage. A disadvantage of this control method is that the controlled value (leakage current) deviates from the measured value (conductivity value), and no measures are taken to prevent damage to the heating element due to overheating caused by air bubbles. If one of the measuring electrodes is a resistance heating coil, this connection does not allow for continuous measurement, but only measurements can be taken in an idle state – water cannot be heated simultaneously.

[0012] Publication document DE102014000536 A1 discloses a measuring device for detecting the electrical conductivity of water in an instant electric water heater, comprising at least two measuring electrodes arranged at a distance in the water flow channel of the instant electric water heater, measuring electronic equipment for providing and evaluating resistance, and a transformer having a primary side and a secondary side, wherein the measuring electronic equipment is connected to the primary side and the two measuring electrodes are connected to the secondary side.

[0013] Publication document WO2021 / 044047A1 discloses a method for controlling an electric water heater, particularly an instantaneous electric water heater, which includes detecting the resistance of a fluid flowing through a water flow channel of the water heater by means of a measuring sensor having two electrodes spaced apart from each other and extending into the water flow channel, for detecting the resistance of the fluid by applying an alternating current between the two electrodes, and controlling the heating power of a heating element based on the detected resistance.

[0014] However, continuous measurements are affected by electromagnetic noise from the operating heating element. Existing technical literature does not address how to eliminate this noise or what other parameters need to be considered to measure resistance and assess conductivity as accurately as possible to meet specification requirements. Summary of the Invention

[0015] The purpose of this invention is to provide an instant electric water heater and its control method, which can solve the above-mentioned problems by continuously measuring the conductivity of water.

[0016] To achieve the above objectives, this disclosure provides an instantaneous electric water heater that heats water by immersing a heating element in the water. It includes a cold water inlet channel, a hot water outlet channel, and a water heating zone disposed between the inlet and outlet channels, which together form a water flow channel through which water flows. At least one bare-wire heating element is located in the water heating zone. The electric water heater also includes a temperature sensor, a pressure sensor, a throttle valve, and a flow limiter controlled by a stepper motor and a flow meter, typically located at the inlet and outlet. The controller uses the temperature sensor located at the outlet to control the operation of the water heater, specifically providing a set desired outlet temperature. Based on the volume and temperature of the water in the water heater, the controller controls the power of the heating element.

[0017] Instantaneous electric water heaters also include first and second measuring electrodes. The two electrodes are spaced apart from each other, and the electrodes can essentially be any conductive component extending into the water flow channel. The water heater also includes a measuring device for measuring water resistance. The measuring device is connected to the electrodes and the controller via connectors and / or wires, and the measurement method includes the calculation of precise parameters of water conductivity.

[0018] Clearly, even if the DC component of the circuit dominates in the event of equipment failure, the measuring device should still operate at the lowest possible voltage to ensure safety. This value should be less than 24V. However, the voltage must be much lower because if copper electrodes (e.g., copper supply tubes) are used, corrosion begins at 0.34V DC. Therefore, using AC voltage prevents electrolysis and allows for reliable and long-term measurements.

[0019] Another issue that needs to be addressed is eliminating electromagnetic interference from the heating element, which is operational during continuous conductivity measurements. Measurements show that as long as the heating element power does not exceed 10 kW, the interference does not significantly affect the measurement signal. However, when the heating element power reaches 27 kW, the electromagnetic interference has a significant impact on the measurement signal.

[0020] Therefore, in order to accurately measure various devices with different power outputs, a resistor is connected in parallel to the measuring electrodes to eliminate electromagnetic interference from the heating element. By testing the measuring device and comparing the measured values ​​with a precise multi-parameter water quality analyzer, the optimal signal-to-noise ratio frequency value and voltage amplitude were determined.

[0021] In some embodiments, the measuring device applies an AC voltage with an amplitude of 0.5V to 1.0V and a frequency of 8 to 12kHz between a pair of measuring electrodes via wires. The use of AC voltage prevents electrolysis and enables reliable and long-term measurements. A resistor with a resistance of 0.5 to 2kΩ is connected in parallel with the pair of measuring electrodes to eliminate electromagnetic interference from the heating element, which operates during continuous conductivity measurements.

[0022] The measuring device is connected to the controller via a four-pin connector (the four pins are for GND, +5V, and two conductors for feedback), and transmits a DC voltage of 0V to 5V to the controller. This DC voltage value corresponds to the converted value of the instantaneous resistance of the water being measured. In some embodiments, the controller uses parameter-determined coefficients to convert the voltage value from the measuring device into a water conductivity value. The parameters used to determine the coefficients include: the resistivity of the material of the metal pipe connected to the cold water inlet channel or the hot water outlet channel, the distance between the first and second measuring electrodes, the measured value of the hot water temperature, the dimensions of the contact areas of the first and second measuring electrodes in direct contact with the water, and the resistance value of the parallel resistor.

[0023] Air bubbles in the water flow channel can be detected so that the resistance between the wires detected by the measuring device is equal to the resistance value of the parallel resistor to eliminate electromagnetic interference. This corresponds to the water conductivity value evaluated by the controller. When the water conductivity limit is exceeded and air bubbles are detected, in both cases, regardless of whether hot water is supplied, the controller will shut off the water heating and disconnect the power to the heating element to protect the user from injury or the heater from damage. If the instantaneous water conductivity value does not exceed a specific threshold stored in the controller's storage circuit, and the water conductivity value does not reflect the presence of air bubbles in the water flow channel, the water is reheated.

[0024] The technical solutions proposed in the above-disclosed embodiments provide a device for continuously measuring the conductivity of water and preventing electric shock caused by water pollution. This device is low in cost because it uses common equipment components and simple measurement circuits. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings related to the present invention described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The image shows the water flow channel of an instant electric water heater with a sensor for detecting the temperature of hot water.

[0027] Figure 2 An example of a measuring electrode is shown, which is formed of a metal tube connected to the water inlet channel of an instant electric water heater;

[0028] Figure 3 A simplified block diagram illustrates an example of the connection between the water flow channel, measuring device, and controller in an instantaneous electric water heater.

[0029] Figure 4 This diagram shows a comparison between the water conductivity measured by a multi-parameter water quality meter and the water conductivity value calculated by the controller. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are included within the scope of protection of the present invention.

[0031] The instant electric water heater 100 series uses a heating element immersed in water to heat water. It includes a cold water inlet channel 1, a hot water outlet channel 2, and a water heating zone 3 located between the cold water inlet channel 1 and the hot water outlet channel 2. The cold water inlet channel 1, the hot water outlet channel 2, and the water heating zone 3 form a water flow channel.

[0032] At least one heating element 10 is disposed in the water heating zone 3, the heating element having a bare wire coil.

[0033] The output of the instantaneous electric water heater 100 is controlled by continuously measuring the hot water temperature in the outlet channel 2 using at least one sensor, such as temperature sensor 5, while the water temperature in the inlet channel 1 can also be measured by another sensor (not shown).

[0034] The controller 9 uses data from the sensor 5 to control the heating power of the heating element 10. In addition to the instantaneous temperature value measured by the temperature sensor 5, other data, such as the water flow rate (not shown) and the target outlet water temperature, are also fed into the control algorithm.

[0035] Since temperature sensor 5 is a common component of any water heater, it is advantageous to use the metal housing of the sensor, which is in direct contact with the water in the outlet channel 2, as the first electrode 20 for measuring the water conductivity. The metal housing of the sensor can be made of any conductive material, most commonly copper, brass, steel, or aluminum. The condition is that all active elements and measuring leads of temperature sensor 5 are insulated from the metal housing of sensor 5 by a non-conductive material.

[0036] The second measuring electrode 30 is preferably a metal pipe connected to the inlet channel 1 or the outlet channel 2, and the metal pipe is grounded according to regulations, such as being connected to the common ground (GND) of the device. The metal pipe is mainly made of copper, but other metal materials can also be used. It is advantageous to use them as electrodes for measuring the conductivity of water because they are in direct contact with water, the resistance of the materials used to manufacture them is known, and they are part of the device. Figure 1 The diagram schematically shows the water flow path of an instant electric water heater equipped with a temperature sensor 5, while also showing in detail the metal casing of the sensor as the first measuring electrode 20 and connected to the measuring wire 6. Figure 2 An example of a second measuring electrode 30 is shown, which is a metal pipe connected to the water inlet channel of an instant electric water heater and is connected to a measuring wire 7.

[0037] The measuring device 8 is used to continuously measure the resistance of water flowing through the water flow channel. It is connected to the first and second measuring electrodes 20 and 30 via two wires 6 and 7, respectively. The two wires 6 and 7 are connected in parallel to a resistor 50 to eliminate electromagnetic interference from the heating element 10. The resistance of the resistor 50 is between 0.5 and 2 kΩ, preferably 1 kΩ. To continuously measure the instantaneous resistance using the measuring device 8, an alternating current is applied between the two wires 6 and 7. The voltage of this alternating current is between 0.5V and 1.0V, and its frequency is between 8 and 12 kHz. Preferably, the alternating current voltage is 0.7V and the frequency is 10 kHz.

[0038] In some embodiments, the measuring device 8 is connected to the controller 9 via a four-pin connector 40 (the four pins are for GND, +5V and two conductors for feedback, respectively). Figure 3 The diagram below shows an example of the connection between the water flow channel, measuring device, and controller in an instantaneous electric water heater. Preferably, the measuring device 8 can be part of the controller 9.

[0039] The 0-5V DC voltage supplied from the measuring device 8 to the controller 9 corresponds to the converted value of the instantaneous resistance of the measured water. In the controller 9, the obtained voltage value is converted into the conductivity value of the water. In some embodiments, the controller 9 uses a parameter-determined coefficient to convert the voltage value from the measuring device 8 into the conductivity value of the water. The parameters used to determine the coefficient include: the resistivity of the material of the metal pipe connected to the cold water input channel 1 or the hot water output channel 2; the distance between the first and second measuring electrodes 20, 30; the measured value of the hot water temperature; the size of the contact area of ​​the first and second measuring electrodes 20, 30 in direct contact with the water; and the resistance value of the parallel resistor 50.

[0040] The controller 9 receives accurate information about the water conductivity at the measured operating temperature through the described circuitry and conversion software, and the device is capable of responding to water quality fluctuations according to international and national safety standards. When a specific water conductivity threshold is exceeded, the controller 9 cuts off the power supply to the heating element 10. Air bubbles in the water flow channel can be detected such that the resistance between the wires 6 and 7 detected by the measuring device 8 is equal to the resistance value of the parallel resistor 50. If the controller 9 detects air bubbles in the water flow channel by evaluating the water conductivity value, in this case, the controller also cuts off the power supply to the heating element 10.

[0041] In both of the above situations, the instantaneous electric water heater can generate a warning signal to the user or display an error message on the water heater's display unit. If the water conductivity value does not exceed a specific threshold stored in the controller's storage circuit, and the water conductivity value does not reflect the presence of air bubbles in the water flow channel, the water is repeatedly heated. Tests have proven that the described water conductivity measurement is very accurate. Figure 4 The results show a comparison between the water conductivity measured by the multi-parameter water quality analyzer (curve 70) and the water conductivity calculated by the controller (curve 80), with the measurement deviation being less than 5%.

[0042] Instantaneous electric water heaters, which heat water via immersion heating elements, require direct contact with hot water for safe operation, necessitating modifications to the equipment used to date. The proposed technical solution provides a low-cost device for continuously measuring water conductivity and preventing electric shock due to water contamination, utilizing common equipment components and simple measurement circuitry.

[0043] In the foregoing description, terms such as "several," "multiple," etc., mean at least two, such as two, three, etc., unless otherwise explicitly specified. In the foregoing disclosure, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, the designation "first," "second," etc., can explicitly or implicitly include at least one of those features. In the foregoing description, terms such as "several," "multiple," etc., mean at least two, such as two, three, etc., unless otherwise explicitly specified.

[0044] In the foregoing disclosure, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0045] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0046] Reference tag list

[0047] 1 – Cold water inlet channel

[0048] 2 – Hot water outlet channel

[0049] 3 – Heating Zone

[0050] 5 – Sensors

[0051] 6, 7 – Wires

[0052] 8 – Measuring device

[0053] 9 – Controller

[0054] 10 – Heating element

[0055] 20 – First measuring electrode

[0056] 30 – Second measuring electrode

[0057] 40 – Connector

[0058] 50-Resistor

[0059] 70 – This displays a curve showing the change in water conductivity with water temperature, the values ​​of which were measured by a multi-parameter measuring device.

[0060] 80 – This displays a curve showing the change in water conductivity with water temperature, the value of which is calculated by the controller.

[0061] 100 – Instantaneous Electric Water Heater

Claims

1. An instantaneous electric water heater (100) that heats water by immersing a heating element in water, comprising: The system includes a cold water inlet channel (1), a hot water outlet channel (2), and a water heating zone (3) located between the cold water inlet channel (1) and the hot water outlet channel (2), wherein the cold water inlet channel (1), the hot water outlet channel (2), and the water heating zone (3) form a water flow channel. At least one heating element (10) is disposed in the water heating zone (3); At least one sensor (5) is used to measure the temperature of hot water; The controller (9) is used to control the heating power of the heating element (10); The first and second measuring electrodes (20, 30), which are set separately, both extend into the water flow channel and are in direct contact with the water therein; Measuring device (8), used for continuously measuring the resistance of water flowing through a water flow channel; characterized in that: The measuring device (8) is connected to the controller (9) and to the first and second measuring electrodes (20, 30) via two wires (6, 7); Two wires (6, 7) are connected in parallel to a resistor (50) to eliminate electromagnetic interference from the heating element (10), the resistance of which is between 0.5 and 2 kΩ; The measuring device (8) is designed to continuously measure the instantaneous resistance between two wires (6, 7) using alternating current; wherein the voltage of the alternating current is between 0.5V and 1.0V and the frequency is between 8 and 12kHz.

2. The instantaneous electric water heater (100) according to claim 1, characterized in that: The resistance of the resistor (50) is 1kΩ.

3. The instantaneous electric water heater (100) according to claim 1, characterized in that: The alternating current has a voltage of 0.7 V and a frequency of 10 kHz.

4. The instantaneous electric water heater (100) according to claim 1, characterized in that: The first measuring electrode (20) is formed by the metal housing of the sensor (5) for measuring the temperature of hot water, and the second measuring electrode (30) is formed by the metal tube connected to the cold water inlet channel (1) or the hot water outlet channel (2), and the second measuring electrode is grounded.

5. A method for controlling an instantaneous electric water heater (100) as described in any one of claims 1 to 4, characterized in that, The method includes the following steps: a) Apply an alternating current between two wires (6, 7), wherein the voltage of the alternating current is between 0.5V and 1.0V and the frequency is between 8 and 12kHz; b) Convert the measured resistance value into a DC voltage of 0V~5V and transmit it to the controller (9); c) The controller (9) converts the obtained voltage value into the conductivity value of water.

6. The method for controlling an instantaneous electric water heater (100) according to claim 5, characterized in that: The alternating current has a voltage of 0.7 V and a frequency of 10 kHz.

7. The method for controlling an instantaneous electric water heater (100) according to claim 5 or 6, characterized in that: The controller (9) uses coefficients determined by parameters to convert the voltage value from the measuring device (8) into the conductivity value of water; wherein the parameters used to determine the coefficients include: The resistivity of the material of the metal pipe connected to the cold water inlet channel (1) or the hot water outlet channel (2), The distance between the first and second measuring electrodes (20, 30), The measured value of the hot water temperature. The dimensions of the contact areas where the first and second measuring electrodes (20, 30) are in direct contact with water. The resistance value of resistor (50).

8. The method for controlling an instantaneous electric water heater (100) according to any one of claims 5 to 7, characterized in that: When the conductivity value of the water in the water flow channel exceeds a water conductivity threshold, the controller (9) interrupts the power supply to the heating element (10).

Images