WATER HEATER AND METHOD OF CONTROLLING SAME

Abstract

A water heater including a cold water intake, a hot water output, a fluid pathway arranged between the cold water intake and the hot water output and adapted to convey water flowing from the cold water intake to the hot water output. A heating element is adapted to heat water that is in the fluid pathway. A power electronics unit is coupled to the heating element. A controller is configured to regulate a temperature of the water in the fluid pathway to an adjustable hot water temperature by controlling the power electronics unit. A water draw-off detector is adapted to detect a water draw-off event and a water sensor is adapted to determine a reference parameter corresponding to a temperature of the water.

Claims

1. A water heater comprising: a cold water intake; a hot water output; a fluid pathway arranged between the cold water intake and the hot water output and adapted to convey water flowing from the cold water intake to the hot water output; a heating element adapted to heat water that is in the fluid pathway; a power electronics unit coupled to the heating element; a controller configured to regulate a temperature of the water in the fluid pathway to an adjustable hot water temperature by controlling the power electronics unit; a water draw-off detector adapted to detect a water draw-off event; a water sensor adapted to determine a reference parameter corresponding to a temperature of the water; and an adjusting means for adjusting between a flow-activated operating mode and a standby operating mode in which the water is kept at a standby temperature.

2. The water heater according to claim 1, wherein the water draw-off detector includes a flow rate sensor, a rocker switch, or a noise sensor.

3. The water heater according to claim 1, wherein the water sensor includes a temperature sensor.

4. The water heater according to claim 1, wherein the water sensor includes a hot water sensor adapted to determine a reference parameter corresponding to a temperature of the water in a vicinity of the hot water output.

5. The water heater according to claim 4, further comprising a cold water sensor adapted to determine a temperature of the water in a vicinity of the cold water intake.

6. The water heater according to claim 1, wherein the adjustable hot water temperature is set to a temperature setpoint value, and wherein the standby temperature is, at most, 10 K above or below the temperature setpoint value.

7. The water heater according to claim 1, wherein the power electronics unit is thermally coupled to a region of the fluid pathway that is upstream from the heating element to thermally regulate the power electronics.

8. The water heater according to claim 1, wherein the power electronics unit comprises: a power triac, a control triac, in particular an opto-triac, which is connected to a gate electrode of the power triac for triggering the power triac, and a voltage-dependent resistor connected in parallel with the control triac.

9. The water heater according to claim 8, wherein a resistor is connected downstream of the control triac and the voltage-dependent resistor short-circuits the power triac to limit the current flowing through the gate electrode of the power triac.

10. The water heater according to claim 9, wherein the downstream resistor is selected according to a maximum operating temperature inside the water heater.

11. The water heater according to claim 8, wherein at least one resistor is arranged in series with the control triac.

12. The water heater according to claim 1, wherein the water heater includes a plurality of modular heating cells, wherein each heating cell includes a cold water intake, a hot water output, a fluid pathway between said cold water intake and said hot water output, a heating element and a power electronics unit, wherein the controller is configured to regulate the temperatures of the water in the fluid pathways through all the heating cells to an adjustable hot water temperature by controlling the power electronics units of all the heating cells.

13. The water heater according to claim 1, wherein the water sensor includes a hot water sensor adapted to determine a reference parameter corresponding to a temperature of the water in the vicinity of the hot water output, further comprising a cold water sensor adapted to determine a temperature of the water in the vicinity of the cold water intake, wherein the controller is configured to: determine a feedforward heating power based on a signal from the water draw-off detector and a temperature difference between the adjustable hot water temperature and a water temperature in a vicinity of the cold water intake, determine a temperature deviation by comparing the temperature in the vicinity of the hot water output with the adjustable hot water temperature, and regulate the heating power in order to reduce the temperature deviation as a control deviation as soon as the temperature deviation is at most a temperature threshold value.

14. The water heater according to claim 1, wherein the controller is configured to: detect an end of a water draw-off operation by sensing a drop in a signal from the water draw-off detector, inhibit restarting of the heating element for a specific period of time, wherein the specific period of time is determined according to the reference parameter corresponding to the water temperature.

15. The water heater according to claim 1, wherein the controller is further configured, in the standby operating mode, to: activate a restart delay to delay restarting of the heating element after each heating operation, deactivate the restart delay responsive to the reference parameter corresponding to the water temperature being lower than the adjustable hot water temperature by a predetermined threshold value, activate the heating element for a predetermined period of time when the restart delay is deactivated.

16. A water heater having a power electronics unit, the power electronics unit comprising: a power triac; a control triac that is connected to a gate electrode of the power triac for triggering the power triac; a voltage-dependent resistor connected in parallel with the control triac; and a resistor that is connected downstream from the control triac and the voltage-dependent resistor and that short-circuits the power triac to limit the voltage through the gate electrode of the power triac.

17. A method of controlling a water heater comprising: determining a feedforward heating power based on a signal from a water draw-off detector and a temperature difference between a temperature setpoint value and a water temperature in a vicinity of a cold water intake; determining a temperature deviation by comparing a temperature in a vicinity of a hot water output with the temperature setpoint value; regulating a heating element to reduce the temperature deviation as a control deviation responsive to the temperature deviation exceeding a temperature threshold value; detecting an end of a water draw-off operation responsive to a drop in the signal from the water draw-off detector; and inhibiting heating of the water heater for a specific period of time having a duration that is based on a temperature of the water; wherein operation of the water heater is adjustable between a flow-activated operating mode and a standby operating mode in which the water is kept at a standby temperature, the method further comprising, in the standby operating mode, the steps of: activating a restart delay in order to delay the restarting of the heating element after each heating operation, deactivating the restart delay responsive to a reference parameter corresponding to the water temperature being lower than the temperature setpoint value by a predetermined threshold value, and activating the heating element for a predetermined period of time when the restart delay is deactivated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG. 1 shows a water heater, in schematic form and by way of example.

[0041] FIG. 2 shows a stack of several heating elements, in schematic form and by way of example.

[0042] FIG. 3 shows, in schematic form and by way of example, a circuit diagram of a power electronics unit with a heating element.

[0043] FIG. 4 shows, in schematic form and by way of example, a flow diagram of a flow-activated operating mode of the water heater.

[0044] FIG. 5 shows, in schematic form and by way of example, a flow diagram of a standby operating mode of the water heater.

DETAILED DESCRIPTION

[0045] As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

[0046] FIG. 1 shows, in schematic form and by way of example, a water heater 1, for example an electronic continuous-flow heater. Water heater 1 includes a cold water intake 2 (also known as a cold water inlet port) and a hot water output 4 (also known as a hot water outlet port) for connecting to a draw-off point. Water heater 1 can be connected in a pressurized or in a non-pressurized form. Water flowing into cold water intake 2 is conducted via a fluid pathway 3 through water heater 1, heated therein and then dispensed via hot water output 4, for example, to a draw-off point. While water flows through water heater 1, a heating element 20 heats the water that is in fluid pathway 3.

[0047] Although a single heating element 20 is shown, the water heater 1 may include a plurality of heating elements 20 that may be arraigned in series. Heating elements 20 may be arranged in individual, modularly arrangeable heating cells. For example, each of the heating elements 20 can allow a power output of between 6 and 12 kW.

[0048] In the view shown by way of example, a power electronics unit 30 coupled to heating element 20 is shown spatially separated. In other embodiments, power electronics unit 30 can also be integrated with heating element 20, as shown, for example, in FIG. 2. Power electronics unit 30 is in thermal contact with a region of fluid pathway 3, such that dissipative heat from power electronics unit 30 is transferred to the water in fluid pathway 3 before it is heated by heating element.

[0049] Although fluid pathway 3 is shown as a linear pathway, the pathway 3 may meander through water heater 1 to save space.

[0050] A controller 40 of water heater 1 is in signal communication with a cold water sensor 44 for detecting the temperature of the cold water flowing in, a water draw-off detection means 42 adapted to detect a flow of water through fluid pathway 3, and a hot water sensor 46 adapted to determine the water temperature in the fluid pathway in the vicinity of the hot water output 4, i.e., after discharge from heating element 20. Water draw-off detection means 42 includes, for example, a flow rate sensor, a rocker switch and/or a noise sensor.

[0051] Controller 40 is configured to control water heater 1 in an operating mode, and in particular to control the temperature of the water in the fluid pathway by controlling the power electronics unit 30 on the basis of a temperature setpoint value. The temperature setpoint value is preferably adjustable.

[0052] The operating mode of water heater 1 that controller 40 allows can be changed using adjusting means 50. That is, the adjusting means 50 is used to change the operating mode of the water heater. The adjusting means 50 can distinguish between operation in a flow-activated operating mode and operation in a standby operating mode. Adjusting means 50 may be provided in the form of a jumper switch, i.e., as a mechanical adjusting means. Alternatively, adjustment can be performed using a software switch, for example, a software flag. In the flow-activated operating mode, a water draw-off event, i.e., the presence of flow through fluid pathway 3, is detected by a flow rate sensor 42, and heating of the water in fluid pathway 3 is triggered only if a water draw-off event is actually present (detected). This prevents any loss of heat due to constant provision of heated water.

[0053] The situation is different in the standby operating mode, in which the temperature of the water in fluid pathway 3 is preferably kept at the temperature setpoint value during the entire operating time. This ensures that hot water is discharged from hot water output 4 even at the start of draw-off. The standby operating mode is suitable in areas of application where there is frequent demand, for example in canteens. The heat losses that then occur are negligible due to frequent use. It is possible, for example, to activate the standby operating mode during particular periods, such as during the periods that a canteen is in operation. In that case, it is possible to switch to the flow-activated operating mode during night-time operation, or alternatively the water heater can be switched off completely when not in use. It is in this sense that the expression “constant provision of heated water” is to be understood.

[0054] Finally, water heater 1 is surrounded by a housing 10 that may also be omitted in other embodiments. Water heater 1 is provided, for example, for three-phase networks in star and delta connection and may be suitable for a power range between 12 and 144 kW.

[0055] FIG. 2 shows part of water heater 1 in schematic form and by way of example. The meandering arrangement of several heating elements 20 is shown here. Based on the arrangement and quantity of multiple heating elements 20, it is possible to adjust the amount of power according to need. Each heating element 20 may be protected by a manual safety switch 100.

[0056] FIG. 3 shows, in schematic form and by way of example, a circuit diagram of a power electronics unit 30. Power electronics unit 30 is arranged between a first conductor L1 and a second conductor L2 and switches a heating element 20 by power triac 32. Power triac 32 is triggered via a control triac 36, which may be an opto-triac, and is connected to the gate electrode of power triac 32. Power triac 32 becomes conductive between the two main electrodes A1 and A2 due to the control current that is then applied to gate electrode G. In order to protect control triac 36, a first resistor R1 and an optional second resistor R2 are connected in series to control triac 36. In this example, the resistors can each be 2.7 kΩ, although other values are also conceivable. A voltage-dependent resistor 34, also called a varistor, is connected in parallel with control triac 36 and protects power electronics unit 30 against sudden overvoltage from the mains, caused, for example, by lightning or by inductive loads starting or stopping.

[0057] However, the disadvantage of this arrangement of voltage-dependent resistor 34 is that, when the ambient temperature in water heater 1 increases, a leakage current through voltage-dependent resistor 34 triggers the gate of power triac 32 in such a way that it fired unintentionally and activates heating element 20. This results in an even higher temperature in the control center of water heater 1. To solve this, a resistor R3 is arranged downstream, which is connected downstream from the control triac and voltage-dependent resistor 34 and which short-circuits control triac 36 in such a way that the current through gate electrode G of power triac 32 is limited.

[0058] By limiting the leakage current occurring, the arrangement of resistor R3 thus prevents the unintentional firing of power triac 32. By selecting the resistance of resistor R3 accordingly, it is possible to set the temperature limit inside water heater 1. A higher resistance value will basically limit the temperature inside the housing to a lower ambient temperature.

[0059] In the following, the flow-activated operating mode is referred to as the “CE” mode, and the standby operating mode is referred to as the “CF” mode.

[0060] FIG. 4 shows, in schematic form and by way of example, a flow diagram of the operation of water heater 1, made possible by controller 40, for example, when adjusting means 50 has adjusted a setting to the flow-activated operating mode, i.e., the CE mode.

[0061] In a first query 410, a test is performed to determine whether a water draw-off event is present or not. The signal from flow sensor 42, for example, is used for this purpose and compared with a predetermined threshold value. Flow rate sensor 42 can output either a binary signal, i.e., “ON” or “OFF”, or a signal that is proportional to the flow rate. Other kinds of signal transmission from flow sensor 42 are also possible. If no water draw-off event is detected, the method starts anew with step 410.

[0062] In the case where the detected flow rate exceeds the threshold value in step 410, it is tested in step 420 whether the water temperature sensed by hot water sensor 46 indicates that the hot water is hot or not. That the hot water is hot is understood here to mean that operation of the water heater did not occur until a short time ago. For example, the fact that the difference between the hot water temperature and the cold water temperature determined by cold water sensor 44 exceeds a predetermined threshold value can be used as an assessment. Alternatively, the hot water temperature can be considered as it compares with the temperature setpoint value that has been set.

[0063] If it is established that the hot water temperature is “hot” in step 420, a delay time is activated in step 430. The delay time delays reactivation of heating element 20 in order to prevent a build-up of the hot water discharge temperature if water draw-offs occur in quick succession.

[0064] The time delay in step 430 is repeated as long the test in step 420 returns a negative result.

[0065] If the test in step 420 is successful, heating operation is switched on in step 440. This means that heating element 20 is operated under the control of controller 40 in such a way that the hot water temperature is as close as possible to the temperature setpoint value.

[0066] The controller may be implemented in such a way that a feedforward heating power is calculated using the flow rate signal and the temperature difference between the cold water intake and the temperature setpoint value. This feedforward heating power is applied via power electronics unit 30 to heating element 20 until the temperature measured at hot water sensor 46 deviates from the temperature setpoint value by a maximum value, for example 10 K. Not until this temperature difference is less than the threshold value is the heating power adjusted and regulated until the control deviation between the hot water temperature and the temperature setpoint value meets the control target, which corresponds, for example, to a deviation of at most 1 K. Heating is continued in step 450 until the drawn-off volumetric flow rate measured by the flow rate sensor is less than the minimum drawn-off volumetric flow rate that has been set, which is the case, for example, when the water draw-off event is terminated.

[0067] FIG. 5 shows, in schematic form and by way of example, a flow diagram in which adjusting means 50 adjusts the operating setting to the “CF” operating mode, i.e., to the standby operating mode. What is shown, therefore, is the control of standby operation, in steps 460 to 480, in addition to the discharge shown in FIG. 4.

[0068] In standby operating mode, the restart delay in step 430 is also active after every heating phase. This corresponds to additional step 460.

[0069] As soon as the temperature of the hot water measured at hot water sensor 46 is more than a predetermined threshold value, for example 10 K, is less than the temperature setpoint value that has been set, the response to the test performed in step 470 is “Yes”. Not until then is step 480 of standby heating operation, i.e., the activation of all the heating elements 20, carried out. Heating elements 20 are preferably activated for a fixed duration, for example for 10 seconds.

[0070] The restart delay according to step 460 and the hysteresis test according to step 470 are repeated.

[0071] While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.