WO2015089553A1

WO2015089553A1 - Electronic controlled instantaneous electric hot water system

Info

Publication number: WO2015089553A1
Application number: PCT/AU2014/001133
Authority: WO
Inventors: Jan Ernst ANTONIDES
Original assignee: Elwa Pty Ltd
Priority date: 2013-12-17
Filing date: 2014-12-17
Publication date: 2015-06-25
Also published as: AU2014366884A1; NZ722353A; AU2014366884B2

Abstract

An electronic instantaneous electric hot water system and method of operation is described and comprises a flow sensor, a heating element and an input temperature sensor for measuring the input temperature of the water. Additionally, a second temperature sensor that measures the output temperature may be included. A user interface receives a set point temperature within a predefined temperature range for an output water temperature and an electronic temperature controller controls the amount of power supplied to the heating element. The electronic temperature controller determines the amount of power to be supplied to using the temperature measured by the input temperature sensor and the flow sensor. The controller is configured to prevent overshoot of the output temperature to prevent scalding. Further, the maximum temperature is predetermined or pre-set and can only be changed using an authorisation code. Control of overshoot and use of an authorisation code for setting the maximum temperature facilitate use in schools, child care centres, hospitals, or other environments.

Description

ELECTRONIC CONTROLLED INSTANTANEOUS ELECTRIC HOT WATER SYSTEM

PRIORITY DOCUMENTS j 0001] The present application claims priority from Australian.. Provisional Patent Applicatio Mo 2013904932 titled "Electronic Controlled Instantaneous Electric Hot Water System" and filed on 17 December 2013, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[00021 The present invention relates to hot water systems. In a particular form, the present invention relates to instantaneous hot water systems,

BACKGROUND

[ 0003] Instantaneous electric hot water systems typically comprise resistive elements which are interleaved with the water path to provide in-situ heating of water to provide on demand hot water. That is, hot water is provided in a short time frame (eg seconds), or instantaneously, compared to storage hot water systems. Thus, bulky and/or inefficient storage tanks are not required, and such instantaneous electric hot water system can be relatively compact in size. Further, such systems are more energy efficient than, storage systems, as there is no energy loss due to storage of hot water, no pumps or circulation systems are required, and they can often be located closer to the point of delivery to reduce the heat loss from pipes from the point of storage to point of delivery. Additionally, as there are fewer losses in the systems the operating temperature (ie temperature the water must be heated to) can be lower producing a safer and more energy efficient system.

[0004] Instantaneous electric hot water systems also provide advantages over instantaneous gas hot water systems as there is no need for a gas supply, pilot lights (which require constant consumption of gas), nor heat loss through flues. Instantaneous electric hot water systems typically use a flow or pressure differential sensor to detect water flow (ie due to the hot water ta being turned on.) and use this detection to trigger immediate heating of the water by a heat exchanger (eg resistive element). Similarly, once the flow stops (ie the tap is turned off) heating is ceased, and thus energy (power) only needs to be supplied to the heating element(s) when water is actually flowing through the system. Additionally, as no flue is required, the systems can be relatively compact and can be fitted almost anywhere including under a sink or immediately adjacent to the delivery point - all that is needed is a water pipe and power supply.

[0005] In the past, absolute fixed temperature control (limiter) of instantaneous electric hot water systems has not been performed, or has been performed relatively coarsely. Typically the- heating elements provide a fixed amount of energy so the output temperature will depend upon the: input temperatu re of the water, the flow rate and the capacity of the heating elements (k Watts or kW). Wh il st this is suitable for many applications, such a lack of control is not suitable in applications to supply hot water for personal hygiene and in situations where children or persons with limited physical or mental capacities are present (eg hospitals, aged care, mental care, or child care centres) and thus may be at risk of scalding if the temperature produced is too high for a sustained period of time. Further, the output temperature of such systems is often adjustable, and thus susceptible to tampering.

[0006 J There is thus a need to provide an instantaneous hot water system with improved temperature con trol, or at least to provide the publi c with a useful alternative.

SUMMARY

1000? I According to a first aspect of the present invention, there is provided an electronically controlled instantaneous electric- hot water system comprising:

a water path;

a flow sensor for detection of water flow rate in the water path in excess of at least one flow rate threshold;

at least one heatin element for heating water flowing through the water path;

an input temperature sensor for measuring the input temperature of the water:

a user interface for receiving a set point temperature within a predefined temperature range- for an output water temperature; and

an electronic temperature controller for controlling the amount of power supplied to the at least one heating element to output water from the water path at the set point temperature obtained from the user interface, wherein the electronic temperature controller determines the amount of power to be supplied to the at least one heating element is based at least in part upon the temperature measured by the input temperature sensor, and the flow sensor output.

[00081 n one form, the user interface is configured to receive an authorisation code to allow an authorised user to set the upper limit of the predefined temperature range. In one form, the upper limit is limited to a maximum value, in one form, th authorisation code also aiiows an authorised user to initiate a disinfectio cycle to disinfect the water heater, fittings and pipework downstream from the water heater. This may be using the same or a different authorisation code. In one form, the disinfection cycle comprises heating water to at least 60°C for at least 10 minutes. After the disinfection cycle the hot water system will remember and fall back to the set point temperature set by the end user and remember and hold the upper limit. Similarly, if the disinfection cycle is interrupted or the temperature chops below 60°C during the 1 minutes cycle, the hot water system will drop back to the stored settings and temperatures. j 0009] In one form, the flow sensor is a pressure differential switch for detecting water flowing through the water path. In one form, the system further comprises a flow restrictor to limit the flow rate of water through the water path to a predefined rate.

[0010] hi one form, the system further comprises a circuit board, wherein circuit board comprises the temperature controller and the input temperature sensor is a ceramic negative temperature coefficient (MTC) resistor fitted on or connected to the circuit board and the circuit board can he fitted on an Met to the water path for cooling purposes. j 00 i 1 j In one form, the system further comprises an output temperature sensor tor measuring the output temperature of the water after heating by the at least one heating element, and wherein the amount of power is determined based at least in part on the measured output temperature of the water. In one form, the electronic temperature controller comprises microcontroller. In one form, the microcontroller controls the amount of power to be supplied to the at least one heating element using a proportional- integral-derivative (PID) algorithm to minimise the error between the output water temperature and the desired temperature obtained from the user interface. In one form, the PID algorithm is configured to minimise overshoot of the output water temperature whilst providing rapid response to minimise the temperature error. In one form, the microcontroller is configured to adjust a gain in PID algorithm in response to the differential between the inlet temperature and the output temperatitre and the magnitude of the water flow rate. In one form, the mic ocontroller is configured estimate the temperature of the at least one heating element based on the elapsed time since last operation of the at least one heating element and one or both of the inlet temperature or output temperature at the time of last operation of the at least one heating element, and the microcontroller further controls the amount of power to be supplied to the at least one heating element based upon the estimated temperature of the at least one heating element. j 0012 ] In one form, the at least one heating element is one, two, three, four or five heating elements.

1_.0013] 1ft one form, the predefined temperature range is. between 35° to 60°.

[0014] According to a second aspect, of the present invention, there is provided a method for controlling the output temperature of .an instantaneous electric hot wate System by controlling the amount of power supplied to at least one heating element in the instantaneous electric hot water system, the method comprising:

receiving a set point temperature within a predefined temperature range for an output water temperature;

receiving a water flow rate through the electric hot water system;

receiving an input temperature;

receiving an output temperature; and determining the amount of power to be supplied to the at least one heating element based at least m part on the water flow rate, input temperature,

[00 ,15] in one form, the method further comprises :

receiving an authorisation code and cheeking if the authorisation code is valid; and

receiving and setting an upper limit for the predefined temperature range if the authorisation code is valid.

[001 ] In one form, the upper limit is limited to a maximum value.

[0017] in one form, the method further comprises:

recei ving an authorisation code and checking if the authorisation code is valid; and

initiatin a disinfection cycle to disinfect the water heater, fixtures and pipework downstream from the water heater.

[0018] In one form, the disinfection cycles comprises heating water to at least 60^"C for at least 10 minutes. After the disinfection cycle the hot water system is configured to remember and fa l back to the set point temperature set by the end user and remember and hold the upper limit. Similarly, if the disinfection cycle is interrupted or the temperature drops below 60°C during the 10 minutes cycle, the water heater controller will drop back to the stored settings and temperatures.

[0019] In one form, determining the amount of power to be supplied to the at least one heating element is performed using a proportionai-iutegral-derivative (PID) algorithm to minimise the error between the output water temperature an the desi red temperature obtained from the user interface. In one form, the PID algorithm is configured to minimise overshoot of the output water temperature whilst providing rapid response to minimise the temperature enOr. In one form, the microcontroller is configured to adjust a gain in PID algorithm in response to the differential . between the inlet temperature and the output temperature and the magnitude of the water flow rate. In one form, the microcontroller is configured to estimate the temperature of the at least one heating element based on the elapsed time since last operation of the at least one heating element and one or both of the inlet temperature or output temperature at the time of last operation of the at least one heating element, and the microcontroller further controls the amount of power to be supplied to the at least one heating element based upon the estimated temperature of the at least one heating element,

[00201 According to a third aspect of the present invention, there is provi ded an electronic temperature controller for controlling the amount of power supplied to the at least one heating element in an instantaneous electric hot water system, the electronic temperature controller comprising a

microcontroller configured to perform the method of the second aspect. [0021.^'] Accordin to a fourth aspect of the present invention, there is provided a processor readable medium comprising instructions for causing a processor to perform the method of the second aspect.

BRIEF DESCRIPTION OF DRAWINGS

[0022] Embodiments of the present invention, will be discussed with reference to the accompanying drawings wherein:

[ 0023] FIGURE 1 is a schematic diagram of an instantaneous electric hot water system according to an embodiment of the present invention;

(0024] FIGU RE 2 is a schematic side view of a water path and heati ng element according to an embodiment of the present invention:

[0025] FIGURE 3 is a plot of the time to scalding as a function of temperature according to AS 3489;

[0026] FIGURE 4 is a schematic diagram of a temperature control circuit according to an embodiment of the present invention;

[0027] FIGURE 5A is a schematic dia gram of a configuration of a single phase instantaneous electric hot wate system according to an embodiment;

[0028] FIGURE 5B is a schematic top view of the instantaneous electric hot water system of Figure 5A;

[0029] FIGURE SC is a schematic side view of the instantaneous electric hot water system of Figure 5 A;

[0030] FIGURE 5D is a schematic bottom view of the instantaneous electric hot water system of Figure 5A;

[0031] FIGURE 5E is a front vie w of the housing and user interface of the instantaneous electric hot water system of Figure 5A;

[0032] FIGURE 6 is a schematic diagram of a first configuration of a tlnee phase instantaneous electric hot water system according to an embodiment;

[0033] FIGURE 7 i a schematic diagram of a Second configuration of a three phase instantaneous electric hot water system according to an embodiment; [0034 ] FIGURE 8A is a plot of output temperature vs time for a range of input temperatures and a first flow rate;

[0035] FIGURE 8B is a plot of output temperature vs time for a range of input temperatures and a second flow rate;

[ 0036] FIGURE 8C is a plot of output temperature vs time for a range of input temperatures and a third flow rate;

[ 0037] FIGURE 9A is a plot of output temperature vs time for a first predefined output temperature for a range of input temperatures;

[0038] FIGURE 9B is a plot of output tempera ture vs rime for a second predefined output temperature for a range of input temperatures;

[ 0039] FIGURE 9C is a plot of output temperature vs time for a tliird predefined output temperature for a range of input temperatures;

[0040] F IGURE- 10 is a graph of the output temperature of water from an instantaneous hot water system according to an embodiment of the inventi on as a function of time for a range of flow rates; and

[0041] FIGURE 1 1 is a flow chart of a method of controlling the output temperature of an instantaneous electric hot water system by controlling t he amount of power supplied to at least one heating element according to an embodiment.

[0042] In tire following description, like reference characters designate like or corresponding parts throughout the drawings.

DESCRIPTION OF EMBODIMENTS

[0043] An. instantaneous electronically controlled electric hot water system with improved temperature control will now be described. Embodiments of the system include a variable set-point, a programmable temperature limiter and a legionella cleaning cycle option. Such systems are suitable for use in supplying hot water in settings where children or persons with limited physical or mental capacities are present (eg hospitals, aged care, mental care, or child care centres) so as to prevent scalding which can occur if persons are exposed to a high temperature for an extended period.

[0044] Australian Standard AS 3489 defines the scalding standard according to the formula s = KV^" x T^" ²'^{· ,SI} where T is the water temperature and s is the time in seconds which the human ski can withstand a particular water temperature before damage is incurred. Hot water systems which comply with AS 3489 are required to produce water at a fixed, non-adjustable operating temperature, such as 38°C, 43°C, 45°C and 50°C (depending upon the application, use environment, or State Health Department requirements), and must not vary from these temperatures in a way that may lead to scalding based upon the above formula. That is, any variation from that temperature must be controlled so that the total integrated deviation does not exceed the scald standard.

J 0045] Referring now to Figure 1, there is shown a schematic diagram of an Instantaneous electric hot water system 100 according to an embodiment of the present invention. Cold water flows into the system through an input pipe 110 and is detected by flow sensor 130. The flow sensor may be a turbine or other type, and in its simplest form is just a flow switch that switches when a predefined flow rate threshold is reached. A flow restnctor may also be included to limit the flow rate of water through the water path to a predefined rate. The temperature controller may use the predefined rate in in the control algorithm. Typical flow switches are venturi based devices in which a venturi pipe generates a pressure drop which i detected by a diaphragm in the pressure differential switch or can be a flow turbine that sends a signal to the control board. The pressure differential switch sensitivity can be adjusted by a central screw within the pressure differential switch. Heating of the water is prevented unless water is detected to be flowing through the water heater by the pressure differential switch or flow sensor. The input from a flow sensor that can communicate more than the two states that a flow switch provides, ma be used as an input to the control algorithm embedded in the temperature controller and used to optimise the response of the controller in relation to water temperature at the outlet.

[0046] Input (or inflowing) water is then directed through the heating module 140 which comprises one or more heating elements to produce heated water in output pipe 170 which can then be supplied to the user . Figure 2 illustrates a side view 200 of a looped water path and integrated heating element according to an embodiment of the present invention. The water path is comprised of a helical (or approximately helical} copper water pipe, which is interleaved with a helical heating element which is supplied with power from leads 221 and 226, Cold water enters the helix at the top input section 21.1 and is

progressively heated as it, flows downward through sections 212, 213, and 214 by heating sections 222, 223, 224 and 225, at which point the heated water leaves vi output pipe section 215. Progressive heating of the water as it passes through the hea ting module is indicated by the shaded arrows.

[00471 Typically, instantaneous hot water systems use one or multiple (eg two, three, four or five or more) resistive elements, which may be jointly or separately controlled. Whilst resistive elements are preferred, other methods and arrangements may be used for heating water such as by embedding heating elements within the water pipes (ie in direct contact with the water) or using an indirect heating method such as using microwave energy or induction to heat the water. [0048] The system, includes a temperature controller 160 which receives input from the flow switch to indicate that water is flowing through the system, and is used to control heati ng of water by the heating module, such as by regulating power supply to the one or more -heating elements. The temperature controller may also receive a flow rate, or in the case that a flow switch is used with, a flow limited, and assumed flow rate may be used based on. the flow signal. The assumed flow rate may be the limited rate, or an offset from the limited rate (eg a midpoint between the turn on rate of the flow switch and the maximum rate due to limiter). The temperature controller also receives temperature measurements from input temperature sensor 120 and optionally an output temperature sensor 150. In one embodiment, the input temperature sensor 120 is located within the flow sensor 130. In one embodiment, the external input temperature sensor can be clipped onto the cold water inlet pipe . The temperature controller then uses these inputs to control the heating clement to produce hot water of the desired temperature. That is, electronic temperatur controller determines the amount of power to be supplied to the heating elements. Preferably the response of the temperature controller is sufficient so that upon turn on, or during use, the total integrated de viation from the desired temperature docs not exceed the AS 3489 scald standard. Typically, the system will also include over temperature protection (not shown) which is provided by a thermal lockout switch that once triggered needs to be manually reset,

[0049] Figure 3 is plot 300 illustrating the AS 3489 scalding curve 310 which illustrates the time to scalding as a function of temperature (s = IO*² x T²' The scalding times for 40°C, 45°C and 50°C correspond to 7794 seconds (or -129 minutes) 473 seconds (-41 minutes) and 38.6 seconds respectively. The dashed line 320 indicates the time to a 2^,ld degree burn for an adult and the solid line 330 indicates the time to a 3^Id degree bum for an adult. Vertical lines mark 45°C and 50°C with the scalding times for 45°C and 50°C marked by intersection points 3.14 and 312.

[0050] To ensure compliance with AS 3489, the total integrated deviation must not exceed the desired steady state temperature for longer than the scald standard (eg 38see for 50°C). This is checked by dividing a test interval (such as first 30 seconds of operation) into discrete sections such as 0.1 s, and measuring the temperature during each interval. For each interval, the scald time for the associated temperature is calculated. To estimate a scald effect, the time interval is divided by the scald time to estimate the percentage of a scald. For example, if the temperature was 55°C during a 0.1ms interval, the scald time for this temperature is 3.7s and thus the scald effect is 0.1/3.7=0.027 of a scald (or -3 of a. full scald). The scald effects are summed over the test interval, and to be compliant the sum must not exceed 1.0 (ie not more than 100% of a scald).

[0051] A significant challenge in providing temperature control in instantaneous electric hot water system occurs when the hot water unit is switched on (ie the hot water tap turned on). The incoming water must be rapidly heated and then maintained at the desired operating temperature. The incoming water temperature can vary significantly. The cold water supply temperature is substantiall lower in winter than in summer. Further variations ma be introduced depending upon the path of the cold water supply and how long ago the hot water system was used (for example exposed pipes may be heated by the sun or there may be residual heat at the heating element from its last operation) in which case the input temperature during the initial demand period may not be stable. Farther, when in use., the flow rates can vary depending upon what other demands are placed on the cold water supply, or other restrictions present in the system (eg due to calcification of taps or pipes).

J 0052] That is, a temperature controller must be able to first heat hot water to a desired temperature, but also provide sufficient control over the heating process to prevent unacceptable overshoot (ie so as to ensure compliance with the scald standard), and be able to react to changes suc as those due to changes in the flow rate or the input temperature of water. f 0053] in order to meet these challenges a temperature controller for an instantaneous hot water .system was developed. In one embodiment, the temperature controller is a digital controller, such as a suitable microcontroller or microcomputer. This provides superior flexibility in programming and optimisation of the control of temperature at the water output. In one embodiment, the microcontroller uses proportional- integrating-derivative (PID) control algorithm to minimise the error between output water temperature and the set temperature. In one embodiment, the PID controllers are controllers that use a proportiona term which provides a correction term based upon the current erro between the output temperature and the set temperature, and integrating term which is based on the accumulation of past errors, and a derivative term which is based upon a prediction of future errors.

[0054] In some embodiments the temperature controller may incorporate fuzzy logic or a variation to the PID control algorithm which seeks to minimise or eliminate overshoot of the outlet temperature over and above the set temperature, whilst still providing rapid response to minimise the temperature error. Such logic and variations may involve adjusting the gain of the controller in response to the differential between inlet and outlet temperature and'or to the magnitude of the water flow rate at that point in time. It ma also adjust the control algorithm in response the temperature of the. heating element, which may remain elevated after recent use, and which may as a result produce outlet water at a temperature in excess of the set temperature. The temperature of the heati ng element may be measured, but in a preferable form, it is calculated based on the elapsed time since fast operation, such as may be readil de termined using the clock on a digital controller, and the conditions at the time of last operations (such as final inlet and outlet temperatures, as may be readily stored on a digital controller.

[0055] A block diagram 400 of the temperature control process is illustrated in Figure 4. Referring to Figure 4 a triac 41 is used to supply power to a load 420 used to heat the water (eg a resistive element). A PID controller 430 is used to control the firing of the triac 432 so as to produce output water at a desired set temperature with a predefined temperature range (eg 35°Cto 60°C) which is stored in the controller 430. A user interface 460 allows a user to set the desired temperature within the range, as well as allowing an. installer to set the limits of the predefined range. In one embodiment, the user interface consists of two momentary switch buttons and a seven segment LED display which displays the current set temperature. On pressing the "up" button the user can increase the set temperature in predefined increments (eg 1°, 2°, 5° or even 10°) and the revised temperature .is displayed. Similarly, the "down" button can be used to adjust the set temperature dovvmvards. The user is prevented from incrementing to a set temperature that exceeds an upper limit that is programmed into the controller by an installer or at the factory by a programming tool or by entry of special coded presses of the buttons.

[0056] The microcontroller may be used to directly drive the user interface, or a separate controller may^¬ be used to drive the user interface and which interfaces with the microcontroller to allow the

microcontroller to receive the desired set temperature from a user, or to allow an authorised installer to adjust the temperature range.

[0057] The set temperature is adjustable over a predefined range to suit different operating needs and environments. In one embodiment, a security means such that this upper limit can only be changed by a technician or other authorised person. In one embodiment, the upper limit can only be set after entering a valid authorisation code. In one embodiment, there is an upper value for the upper limit of the

temperature range, to ensure that very hot water can never be discharged. Further, the same authorisation code or another authorisation code may be used to initiate a disiniection cycle to disinfect the water heater, fittings (eg tapware) and pipework downstream from the water heater, so as to kill off legionella bacteria and/or other bacteria, in one form, the disinfection cycles comprises heating water to at least 60°C for at least 10 minutes (this is the current Health requirement in ail States in Australia). .For example, the manufacturer or installer may be provided with the authorisation code for setting the maximum temperature, whilst a supervisor user (or users) at the installation location may be provided with a separate authorisation code for initiating the disinfection cycle. This prevents users at the installation site from adjusting the maximum temperature whilst allowing them to initiate disinfection cycles. The exact disinfection cycle may be selected based upon requirements or regulations issued from a Government Health Department. After the disinfection cycle the hot water system will remember and fail back to the user defined set point temperature set by the end user and remember and hold the upper limit (eg set by the manufacturer or installer). Similarl if the disinfection cycle is interrupted or the temperature drops below 60°C during the 10 minutes cycle, the hot water system will drop back to the stored settings and temperatures.

[0058] The system may fiirther comprise a circuit board, wherein the circuit board comprises the temperature controller and one or more components for the adjustment and storing of the upper limit for the set temperature. These components may allow the system to be made tamper proof as the upper limit for the set temperature is defined in the programming. In one embodiment, a programming tool may be π

^•required to alter the value stored in these components. In one embodiment, a predefined code must be entered to the eompouent(s) to vary the set temperature upper limi t. In one embodiment, the

microcontroller has a communications port to allow an installer to connect to the microcontroller. The communications port may be wired or wireless (eg a short range RF protocol sBCh as Bluetooth or infrared protocol such as IRDA). The microcontroller is configured to limit access to the microcontroller functionality, such as control the temperature range limits, initiate a disinfection cycle or update firmware or other parameters, via an authorisation code or similar security means such as a password or cryptographic based access control, or even insertion of a security key or specialist mechanical device. A user interface may be provided to allow a user to set the temperature within the predefined range, or to request a disinfection cycle (including inputting an authorisation code). The authorisation code (or codes) may be numeric, alphanumeric, or a sequence of input button presses. For example, in the example discussed above in which the input interface is an LCD screen with an up arrow and a down arrow, the up could map to 1 and down to 0 and the authorisation code is a fixed length binary sequence. A sequence of up and down key presses can then be used to enter the authorisation code.

[0059| A flow rate sensor 450 communicates with the controller 430 and is used in the control algorithm to vary the amount of heating it demands from the load 420 via the triac 410 to optimise the control of the water outlet temperature (T outlet). Similarly, a temperature sensor measurin water inlet temperature (T inlet) is input to the controller 430 and used in the control algorithm to vary the amount of heating it demands from the load 420 via the triac 410 to optimise the control of the water outlet temperature (T outlet). The flow sensor 450 and inlet temperature inputs to the control algorithm thus improves the response time of the controller to ensure the system complies with the scald standard for a range of input flow rates and temperatures.

I^'0060^'l The above temperature control circuit may be provided on a printed circuit board (PCB, also referred to as the control board). In addition (or as part of) the temperature control circuit, the circuit board also includes one or more components for defining a reference signal (eg reference current or voltage) corresponding to the set temperature. That is, the reference temperature is defined on the control board, and so the output temperature can onl be effectively changed by replacing the circuit board, which effectively makes the system tamper proof.

[0061 [ in one embodiment, the circuit board comprises the temperature controller and the input temperature sensor which is a ceramic negative temperature coefficient (NTC) resistor fitted to the circuit board, and the circuit board is located over an inlet to the water path. Optionally, a temperature sensor may also measure the outlet (or output) water temperature. In one aspect the output temperature sensor is also a ceramic negative temperature coefficient (NTC) resistor. This can be fitted on or connected to the circuit board, and the circuit board is fitted on the water path for cooling purposes. j 0062 ] Embodiments of the system can use one, two or three heating, elements or more, A cascading control can be used to switching 1 or more (eg 2, 3, 4, 5, ...) elements on/off based on the inlet water temperature, and trimming the outlet water temperature to comply within the limits as defined in the AS3498 to prevent people from scalding. The amount of power (current) applied to each element is variable depending on the water-flow, model (k Watt loading) and the outlet temperatiffe limit required.

[^'0063 ] In one example, the system is a 3-phase 1 Amp model with a maximum flow rate of 6 Itr min, and the maximum temperature change per element (AT) is 25°C (3 elements of 3.8 k Watt/415 or

240Volt).

[0064] Fo an outlet temperature limited to 50°C with a ΔΤ of 25°C the system is operated as fellows;

Element # 1 to switch off at an inlet temperature of 50-l6^~32°C;

Element # 2 to switch off at an inlet temperature of 50-8=41° C; and

Element # 3 trim/pulse to set-point.

[0065] For an outlet temperature limited to 45 °C with a AT of 25°C the system is operated as follows:

Element # 1 to switch off at an inlet temperature of 45-] 6=25°C;

Element # 2 to switch off at a inlet temperature of 45-8=38°C; and

Element # 3 trim/pulse to set-point. j 0066 J For an outlet temperature limited to 40°C with a AT of 25°C the system is operated as follows;

Element # 1 to switch off at an inlet temperature of 40-16=22°C;

Element # 2 to switch off at an inlet temperature of 40-8-31 ^GC; and

Element # 3 trim pulse to set-point. j 0067 j In another example, the system is 2 -phase 20Amp model limited to 5 Itr/min and the AT is 12.5^DC per element (2 elements of 4,5 k Watt/24 Volt).

[006 1 For an outlet temperature limited to 50*C with a AT of 25° the system is operated as follows:

Element # 1 to switch off at an inlet temperature of 50-12.5=37.5°C; and

Element # 2 to trim/puise to set-point.

[0069] For an outlet temperature limited to 45°C with a ΔΤ of 25°C the system is operated as follows:

Element # 1 to switch off at an inlet temperature of 45-12.5=31.5°C; and

Element # 2 to trim/pulse to set-point.

[0070] For an outlet temperature limited to 40°C with a AT of 25°C the system, is operated as follows:

Element # 1 to switch off at an inlet temperature of 40- 12..5=25.5°C ; and Element # 2 to trim/piiils to set-point.

[0071] In another example, the system is a 1 -phase 16 Amp model in which the flow rate is limited to 1.8 Itr/min and the ΔΤ is 25°C per element (I element of 3.5 k Watt/240 Volt). j 0072] For an outlet temperature limited to 38. 43, 45 or 50°C with a ΔΤ of 25°C the system is operated as follows:

Element # 1 to trim pulse to set-point.

[0073] In the above examples, it is assumed that the power supply voltage 415/240Volt at 50Hz. In the above embodiments, at least one of the elements is controlled by a Triac or solid state relay. The microcontroller on the PCB can be configured to support all of the above examples, for example covering a range of 3.5 k W (single phase) to 27kW (three phase) systems. Figure 5A is a schematic diagram 500 of a configuration of a single phase instantaneous electric hot water system according to an embodiment. Art inlet pipe 1 10 delivers wate to the wate flow sensor 130 which also contains the first input temperature sensor 120. The water then flows past the PCB-1 161 (the Triac control board) connected to PCB-3. the user control panel in the fron t cover of the water heater implementing the temperature control method, and into the heat exchange housing 162. Power is supplied by PCB 161 to heating element(s) 142 and capacitors (on a separate PCB board) 164 An over- temperature cut-out li miter 166 and an output temperature sensor 150 are also provided. Heated water is provided via outlet pipe 170. Figures 5B, 5C, and 5D are schematic top 510, side 520 and bottom 530 views respectively of the instantaneous electric hot water system of Figure 5A. Figure 5E is a front view 540 of the housing 542 and user interface 460 of the instantaneous electric hot water system of Figure 5 A. Inlet 1 10 and outlet 170 pipe connectors are located at the base, and an o verflow pipe 544 is located at the top right. The front of the housing includes a user interface panel 460 comprising a LED display 462 to display the current temperature and buttons 464 comprising momen tary switch u and down buttons and an on/off power button. Figure 6 is a schematic diagram of the same system described above for a three phase instantaneous electric hot water system according to an embodiment. In this embodiment a terminal block 167 received three phase power which is provided to the PCB board 1 .1 and capacitor 162 and transformer 163 circuits three or five resistive heating elements Rl , R2, R3, 4 and R5 are configured as shown to provide 12kW or l.5kW systems. Simi larly Figure 7 is a schematic diagram of a second configuration of a three phase instantaneous electric hot wate system according to an embodiment. In thi embodiment three or five resistive heating elements R l, R2, R3, R4 and R5 are again used but configured as shown to provide J 8kW, 21kW or 24k W systems.

[ 0074] As would be understood by the person skilled in the art, for a fixed amount of input heating energy and a fixed length water path, the rate of heating and the output temperature will decrease with increasing flow rates. In practice the maximum amount of heat that can be delivered depends upon the capacity of the heating element (ie power output and/or number of heating el ements), and thus at high flow rates this may prevent reaching a desired output temperature. This effect is illustrated in Figures A to 8C, which are plots of output temperature vs time for a range of input temperatures and flow rates for a system designed to operate at a flow rate of 5L/m. Figure 8A is a plot 910 of output temperature vs time for a first flow rate of 4.3L m (20% below the design rate) for water with an. input temperature of 15°C 1.2, 20°C 14 and 25°C 16. Similarly, Figure 8B is a plot 920 of output tempera ture vs time for a second flow rate of 5.1 L/m for water with an input temperature of 15°C 922, 20°C 924 and 25°C 926, and Figure 8C is a plot 930 of output temperature vs time for a third flow rate of 6.1 L/m (20% above design flow rate) for water with an input temperature of 15°C 932, 20°C 934 and 25°C 936. For example, at an input temperature of 25°C, the output temperature varies: between about 51 °C for a flow rate of 4.3 L/m down to 44°C for a flow rate of 6.1 L/m. Other flow rates can be used. Typically, a system will be designed to operate at a design or preferred flow rate, and a flow restnctor is preferably included to limit flows to a maximum flow rate such as the design flow rate, or some limit based upon the design flow rate, to ensure that the desired output temperature can be achieved by the system. Accordingly, prior to installation, it is preferable to determine (either measure or estimate) the flow rate so that an appropriate system which matches the flow rate can. be selected for installation (eg such as one of the systems illustrated in Figures 5-7). Further, the differential flow switch can be used to set a minimum flow' rate, below which no heatin is performed. Further, in other embodiments, more complicated flow sensors cart also be incorporated to ensure that heating is only allowed during a defined range of flow rates.

[0075 ] However, it is noted that at any flow rate the controller will produce scald compliant output temperatures if the temperature limiter has been programmed for a temperature limit as per AS3498 or temperatures required b additional regulations from local health departments This is illustrated in Figures 9 A, 9B and 9C, which are plots of output temperature vs time for a range of predefined output temperatures for input temperatures of f 5°C and 25°C at the optimal flow rate ( 5.0L/m in this embodiment). Figure A is a plot 1000 illustrating output temperature as a function of time for input temperatures of 25°C 1002 and 15°C 1.004 for a first set point of 40'³C. Similarly, Figure 9.B is a plot 1 10 illustrating output temperature as a function of time for input temperatures of 25 C 1012 and 1 °C 1014 for a second set point of 45°C, and Figure 9C is a plot 1030 illustrating output temperature as a function of time for input temperatures of 25°C 1 32 and 15°C 1034 for a third set point of 50°C. Other input temperatures and set point temperatures can be used. These plots illustrate that temperature control which doe not exceed the scald standard can be quickly performed for a range of input temperatures. This is further ill ustrated in Figure 1 , which shows a graph 1 100 of the output temperature of water as a function of time for input temperatures of 15° C 102, 20°C 1104, and 25°C 1 106, each at a fixed flow rate of 2,2 litres per minute of a. system with a desired output temperature of 50^C'C. Figure 10 indicates that stable control of temperature is achieved after about 30 seconds in all cases. In the ease that the input temperature was 25°C, the output temperature initially overshot the target temperature by approximately 2°C, but was brought, back down to the target temperature within about 10 seconds and well within the scald time of 39 seconds for this output temperature (50°C).

[0076] Figure 1 1 is a flow chart 1100 of a method of controlling the output temperature of an instantaneou s electric hot water system by controlling the amount of power supplied to at least one heating element according to an embodiment. The method comprises the steps of:

receiving a set point temperature within a predefined temperature range fo an output wate temperature 1102;

receiving a water flow rate through the electric hot water system 1104;

receiving an input temperature 1 1 6;

receiving an output temperature 1.108; and

determining the amount of power to be supplied to the at least one heating element based at least in part on the water flow rate, input temperature 1 1 10.

[0077] The system described herein also has the advantage of being tamper proof, (in respect, of the output temperature) as the maximum temperature (ie th desired output temperature) is limited within a predefined range, and the temperature controller is able to safely produce this output temperature for a range in input flow rates and. temperatures. That is, even if a user opens u the physical unit they to gain access to the circuit elements they cannot alter the maximum temperature. This effectively makes the system^' tamper proof to users (or users wi thout the authorisation code), which is an important requirement when producin systems for use in schools, child care centres, hospitals, or other environments where the public or users of the system could attempt to tamper with the temperature control .

[00781 The system and heat controller described herein can be used for effectively providing an instantaneous electric hot water system with improved fixed temperature control, and which ca provide temperature control that satisfies the AS 3489 scalding standard. This enables wider use of instantaneous electric hot water system in locations where children or persons with limited physical or mental capacities are present (eg hospitals, aged care, menial care, or child care centres). Further, though the use of an electronic temperature controller with a security^■means to prevent users from setting the temperature outside of a predefined range (ie oniy an installer/technician can define the limits of the settable range for users), the system has the additional advantage of being tamper proof.

[0079] Those of skill in the art would understand tha t information and signals may be represented, using any of a variety of technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or an combination thereof. [0080] Those of skill in the art would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchange ability of hardware, and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not he interpreted as causing a departure from the scope of the present invention,

} 0081 J The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. For a hardware implementation, processi ng may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic device (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. Software modules, also known as computer programs, computer codes, or instructions, may contain a number a number of source code or object code segments or instructions, and may reside in any computer readable medium such as a RAM memory, flash memory, ROM memory, EPROM memory, registers, hard disk, a removable disk, a CD- ROM, a DVD-ROM or any other form of computer readable medium. In the alternative, the computer readable medium may be integral to the processor. The processor and the computer readable medium may reside in an ASIC or related device. The software codes may be stored in a memory unit and executed by a processor. The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.

I ^"0082-1 Throughout the specification and the claims that follow, unless the context requires otherwise, the words "comprise" and "include" and variations such as "comprising" and "including" will be understood t imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers..

[0083] The reference to any prior art in this specification is not, arid should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common genera ! knowledge.

[0084] It will be appreciated by those skilled in the art mat- the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the invention is not iimtted to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.

Claims

1. An instantaneous electric hot water system comprising:

a water path;

at least one heating element for heating water flowing through the water path;

an input temperature sensor for measuring the input temperature of the water;

a user interface for receiving a set point temperature within a predefined temperature range for an output water temperature; and

an electronic temperature controller for controlling the amount of power supplied to the at least one heating element to output water from the water path at the set point temperature obtained from the user interface, wherein the electronic temperature controller determines the amount of power to be supplied to the at least one heating element based at least in part upon the temperature measured by the input temperature sensor and the flow sensor.

2. The system as claimed in claim 1, wherein the user interface is configured- to receive an.

authorisation code to allow an authorised user to set the upper limit of the predefined temperature range.

3. The system as claimed in claim 2, wherein the upper limit is limited to a maximum value.

4. The system as claimed in claim 2 or 3, wherein the authorisation code also allows an authorised user to mitiate a disinfection cycle to disinfect the water heater, fittings and pipework downstream from the water heater.

5. The system as claimed in claim 4, wherein the disinfection cycles comprises heating water to at least 60"C for at least 10 minutes,

6. The system as claimed in any preceding claim, wherein the flow sensor is a pressure differential switch for detecting water flowing through the wate path.

7. The system as claimed in any preceding claim, further comprising a flow restrietor to limit the flow rate of water through, the water path to a predefined rate .

8. The system as claimed in any preceding claim, further comprising a circuit hoard, wherein circuit board comprises the temperature controller and the input temperature sensor is a ceramic negati ve temperature coefficient (NTC) resistor fitted on or connected to the circuit board and the circuit board is fitted on an inlet to the water path for cooling purposes.

9. The system as claimed in in any preceding claim, further comprising an output temperature sensor for measuring th e output temperature of the water after heating by the at least one heating el ement, and wherein the amount of power is determined ba sed at least in part on the measured output temperature of the water.

10. The system as claimed in claim 9, wherein the electronic temperature controller comprises a microcontroller.

1 1. The system as claimed in claim 10, wherein the microcontroller controls the amount of power to be supplied to the at least one heating element using a proportional -integral-derivative (P!D) algorithm to minimise the error between the output water temperature and the desired temperature obtained from the user interface.

12. The system as claimed in claim 11 , wherein the PID algorithm is configured to minimise o vershoot of the output water temperature whilst providing rapid response to minimise the temperature error.

13. The system as claimed in claim 11 , wherein the microcontroller is configured to adjust a gain in PlD algorithm in response to the differential between the inlet temperature and the output temperature and the magnitude of the water flow rate,

14. The system as claimed in claim 10, wherein the microcontroller is configured estimate the temperature of the at least one heating element based on the elapsed time since last operation of the at least one heating element and one or both of the inlet temperature or output temperature at the time of last operation of the at l east one heating element, and the microcontroller further con trols the amount of power to be supplied to the at least one heating element based upon the estimated temperature of the at least one heating element.

15. The system as claimed in any preceding claim, wherein the at least one heating element is one, two, three, four or fi ve heating elements.

16. The system as claimed in. any preceding claim, wherei the predefined temperature range is between 35" to 60°.

17. A method for controlling the output temperature of an. instantaneous electric hot water system by controll ing the amount of power supplied to at least one heating element in the instantaneous electric hot water system, the method comprising:

receiving a set point temperature within a predefined temperature range for an output wate temperature;

receiving a water flow rate through the electric hot water system;

receiving an input temperature;

recei ving an output temperature; and

determining the amount of power to be supplied to the at least on heating element based at least in part on the water flow rate and the input temperature,

1 8. The method as claimed in claim 17, further comprising:

receiving an authorisation code and checking if the authorisation code is valid; and

recei ving and setting an upper l imit for the predefined temperature range if the authorisation code is valid...

1 . The method as claimed in claim 18, wherein the upper limit is limited to a maximum value.

20. The method as claimed in claim 17, furthe comprising:

recei ving an authorisation code and checking if the authorisation code is valid;

initiate a disinfection cycle to disinfect the water heater, fittings and pipework downstream from the water heater.

21. The method as claimed in claim 20, wherein the disinfection cycles comprises heating water to at least <^">^{)"(^'' for at leastlO minutes.

22. The method as claimed in claim 17, wherein determining the amount of power to be supplied to the at least one heating element is performed using a proportional-integral-dcrivative (PID) algorithm to minimise the error hetween the output water temperature and the desired temperature obtained from the user interface.

23. The method as claimed in claim 22, wherein the PID algorithm is configured to minimise o vershoot of the output water temperature whilst providing rapid response to minimise the temperature error.

24. The method as claimed m claim 23, wherein the microcontroller is configured to adjust gain in PID algorithm in response to the differential between the inlet temperature and the output temperature and the magnitude of the water flow rate.

25. The method as claimed in claim 22, wherein the microcontroller is configured to estimate the temperatu re of the at least one heating element based on the elapsed time since last operation of the at leas t one heating element and one or both of the inlet temperature or ou tput temperature- at the time of last operation of the at least one heating element, and the microcontroller further controls the amount of power to be supplied to the at least one heating element based upon the estimated temperature of the at least one heating element.

26. An elec tronic temperature controller for controlling the amount of power supplied to the at least one heating element: in an instantaneous eleetric hot water system, the electronic temperature controller comprising a microcontroller configured to perform the method of any one of claims 17 to 25.

27. A processor readable medium comprising instructions for causing a processor to perform the method of any one of claims 17 to 25.