A WATER HEATER CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from South African provisional patent application number 2015/03775 filed on 27 May 2015, which is incorporated by reference herein. FIELD OF THE INVENTION

This invention relates to a system and method for improving efficiency of a water heater, such as an electrical water heater, by determining a customised heating schedule for the water heater. BACKGROUND TO THE INVENTION

Electrical water heaters are widely used in numerous countries to heat water for household consumption. South Africa is one such country, and has approximately 5.4 million electrical water heaters with water heating being responsible for about 7% of its average electricity demand, and 20% of the residential demand. However, during peak hours, it constitutes between 30% and 50% of the residential demand.

Part of the energy consumed by electrical water heaters is to replenish heat dissipated to the environment. Standing losses such as these could be as much 2.5 kWh per day. These standing losses can be greatly reduced if a timer control is applied to only heat the water before warm water is needed.

Demand side management aims to flatten a utility's demand curve by shifting customer energy usage and reducing losses on the load side. This is advantageous to utilities as it allows for the deferral of infrastructure development to increase generation capacity by, instead, reducing the demand. Electrical water heaters are well-suited to demand side management programs as they are able to store energy. However, many of these devices are mismanaged and suffer from large standing losses as warm water is available throughout the day, even for extended periods where no usage occurs.

Demand side management control techniques and programs have been created to more effectively manage the energy consumption of residential electrical water heaters. However, for these controllers or programs to be effective, an accurate water usage profile is essential to coordinate the switching times for electrical water heaters. This is because consumer usage patterns vary between users, seasonally, and between regions. For example, in South Africa, it was found that warm water consumption increases by up to 70% from summer to winter and that high-income households consume up to four times more warm water per person than low-income households.

For indirect load management programs, where consumers are responsible for the control of their devices, customer participation is important. Users need to be able to control and understand their energy consumption in a simple and convenient manner. This is not currently the case with electrical water heaters, which are often positioned in hard to reach locations such as on roofs or in attics. Additionally, users do not always know the best means of controlling their electrical water heaters to save energy. For example, a user may not know when to switch it on and off to reduce energy consumption but still have warm water on demand when needed. One way of detecting warm water consumption patterns of individual electrical water heaters is to use water flow meters in the inlet or outlet pipes of the water heaters. However, such flow meters are expensive and their installation is labour intensive.

This invention aims to address these problems, as least to some extent.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a method for determining a customised heating schedule for a water heater, comprising:

by means of a sensor non-invasively arranged at an outlet pipe of the water heater, periodically sampling an output signal of the sensor;

in response to detecting a first predefined signal, identifying a hot water usage event as having begun;

in response to detecting a second predefined signal, identifying a hot water usage event as having ended;

recording the time and duration of each hot water usage event in a digital memory;

updating a usage profile of the water heater, the usage profile indicating usage times at which water in the heater should be at a usage temperature; and based on the usage profile, determining a customised heating schedule for the water heater.

Further features provide for determining the customised heating schedule to include:

retrieving the recorded time and duration of previous usage events for each day of the week for a number of preceding weeks;

determining expected hot water events on a particular day of the week by calculating an average distribution of hot water events for that day of the week based on the previous usage events; and

determining the customised heating schedule so that sufficient energy will be stored in the water heater to supply the expected hot water events on that particular day of the week.

In one embodiment, the sensor is a temperature sensor with the output signal thereof representing the temperature of the outer surface of the outlet pipe; the temperature sensor being secured to the outer surface of the outlet pipe; the first predefined signal being a predefined rate of rise in the temperature over two or more successive samples; and the second predefined signal being a predefined rate of drop in the temperature value over two or more successive samples.

In an alternative embodiment, the sensor is a flow sensor with the output signal thereof representing the rate of flow through the outlet pipe; the first predefined signal being a predefined upper flow rate threshold; the second predefined signal being a predefined lower flow rate threshold; and the flow sensor being selected from the group consisting of an ultrasonic flow sensor, a piezoelectric flow sensor, and an electromagnetic flow sensor. In a further alternative embodiment, the sensor is a vibration sensor with the output signal thereof representing a vibration magnitude of the outlet pipe; the first predefined signal being a predefined upper vibration magnitude threshold; the second predefined signal being a predefined lower vibration magnitude threshold; and the vibration sensor being selected from the group consisting of a passive vibration sensor and a digital accelerometer.

A further feature provides for the method to include controlling an energy supply of the water heater according to the customised heating schedule, such that overall energy consumption is reduced while ensuring that the water is at the usage temperature at the usage times. The energy supply of the water heater may be controlled by switching on the energy supply for a period of time before expected usage events. In one embodiment, the water heater is an electrical water heater and the energy supply is an electricity supply. In one embodiment, the method may include an initial step of retrofitting an existing water heater with a temperature sensor by attaching the temperature sensor to the outer surface of the outlet pipe of the water heater. In an alternative embodiment, the method may include an initial step of retrofitting an existing water heater with a flow sensor by attaching the flow sensor to the outer surface of the outlet pipe of the water heater.

In a further alternative embodiment, the method may include an initial step of retrofitting an existing water heater with a vibration sensor by attaching the vibration sensor to the outer surface of the outlet pipe of the water heater.

A further feature provides for the usage profile to indicate different usage times for different days of the week. The usage profile may be updated on a periodic basis, such as once per day or once per week, to account for changes in the measured time and duration of hot water events on a previous day or on a specific day of the week in a previous week.

Further features provide for the temperature of the outlet pipe to be sampled at a preconfigured sampling period; for the sampling period to be between 30 seconds and 5 minutes; preferably for the sampling period to be between 50 seconds and 70 seconds.

In one embodiment, the predefined rate of rise in the sampled temperature is greater or equal to four degrees Celsius across two successive sample values and the predefined rate of drop in the sampled temperature is greater or equal to two degrees Celsius across seven successive sample values.

The invention extends to a system for determining a customised heating schedule for a water heater, the system including a control unit having:

a signal receiving component for receiving, from a sensor from a sensor non-invasively arranged at an outlet pipe of the water heater, periodic sensor output signals;

a hot water usage event detection component for detecting the beginning and end of a hot water usage event;

a memory component for storing the time and duration of each hot water usage event, and for storing a usage profile indicating usage times at which water in the heater should be at a usage temperature;

a usage profile updating component for updating the user profile based on the time and duration of the time and duration of hot water usage events; and a scheduling component for determining a customised heating schedule based on the usage profile.

In one embodiment, the signal receiving component is a temperature receiving component for receiving, from a temperature sensor attached to an outer surface of an outlet pipe of the water heater, periodic temperature sample values of the temperature of the outlet pipe.

In an alternative embodiment, the signal receiving component is a flow rate receiving component for receiving, from a flow sensor attached to an outer surface of an outlet pipe of the water heater, periodic sample values of the flow rate in the outlet pipe.

In a further alternative embodiment, the signal receiving component is a vibration magnitude receiving component for receiving, from a vibration sensor attached to an outer surface of an outlet pipe of the water heater, periodic sample values of the vibration magnitude of the outlet pipe.

Further features provides for the control unit to include an energy supply control component for controlling an energy supply of the water heater so that overall energy consumption is reduced while ensuring that the water is at the usage temperature at the usage time. The energy supply of the water heater may be controlled by switching on the energy supply for a period of time before expected usage events. In one embodiment, the water heater is an electrical water heater and the energy supply is an electricity supply.

The invention extends to a method of improving overall efficiency of a water heater, comprising the steps of:

non-invasively arranging a sensor at an outlet pipe of a hot water heater;

periodically sampling an output signal of the sensor;

detecting a first predefined signal;

in response to detecting the first predefined signal, identifying a hot water usage event as having begun;

detecting a second predefined signal;

in response to detecting the second predefined signal, identifying a hot water usage event as having ended;

recording the time and duration of each hot water event in a digital memory;

updating a usage profile of the water heater, the usage profile indicating usage times at which water in the heater should be at a usage temperature;

based on the usage profile, determining a customised heating schedule for the water heater; and controlling an energy supply of the water heater according to the customised heating schedule, so that overall energy consumption is reduced while ensuring that the water is at the usage temperature at the usage times. In one embodiment, the sensor is a temperature sensor with the output signal thereof representing the temperature of the outer surface of the outlet pipe; the temperature sensor being secured to the outer surface of the outlet pipe; the step of detecting a predefined first signal comprises detecting a predefined rate of rise in the temperature value over two or more successive samples; and the step of detecting a second predefined signal comprises detecting a predefined rate of drop in the temperature value over two or more successive samples.

In an alternative embodiment, the sensor is a flow sensor with the output signal thereof representing the rate of flow through the outlet pipe and the step of detecting a predefined first signal comprises detecting a predefined upper flow rate threshold; and the step of detecting a predefined second signal comprises detecting a predefined lower flow rate threshold.

In a further alternative embodiment, the sensor is a vibration sensor with the output signal thereof representing the vibration magnitude of the outlet pipe and the step of detecting a predefined first signal comprises detecting a predefined upper vibration magnitude threshold; and the step of detecting a predefined second signal comprises detecting a predefined lower vibration magnitude threshold.

The energy supply of the water heater may be controlled by switching on the energy supply for a period of time before expected usage events. In one embodiment, the water heater is an electrical water heater and the energy supply is an electricity supply.

The invention extends to a method for determining a customised heating schedule for a water heater, comprising :

identifying and recording water usage events with respect to the water heater; and using the recorded usage events to determine a customised heating schedule for the water heater, characterised in that the usage events are identified by means of a temperature sensor that is attached to an outlet pipe of the water heater.

In one embodiment, historical water usage data, for a particular day of week, includes data for the preceding four weeks.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: is a schematic representation of a system for determining a customised heating schedule for a water heater in accordance with an embodiment of the invention; is a block diagram showing an embodiment of a control unit of Figure 1 ; is a graph showing an example of temperature reading obtained by a temperature sensor of Figure 1 ; is a graph showing a second example of temperature readings obtained by the temperature sensor of Figure 1 ; is a flow diagram showing a method of determining usage events using the control unit of Figure 2; is a schematic representation of a system for determining a customised heating schedule for a water heater in accordance with a further embodiment of the invention; is a block diagram showing an embodiment of a control unit of Figure 6; is a graph showing an example of flow rate readings obtained by the flow sensor of Figure 6; and is a flow diagram showing a method of determining usage events using the control unit of Figure 7.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

Embodiments described herein provide a method and system for determining a customised heating schedule for a water heater. A sensor is non-invasively arranged at an outlet pipe of the water heater, the output signal of which is periodically sampled. Once a first predefined signal is detected, the start of a hot water usage event is identified. Furthermore, once a second predefined signal is detected, the end of a hot water usage event is identified. The time at which each water usage event occurs, and the duration thereof, is recorded in a digital memory. A usage profile of the water heater is updated. The usage profile indicates usage times at which water in the heater should be at a desired usage temperature. Based on the usage profile, a customised heating schedule is determined for the water heater.

In one exemplary embodiment, the sensor is a temperature sensor. The temperature sensor may be secured to the outer surface of the outlet pipe. The output signal of the temperature sensor represents the temperature of an outer surface of the outlet pipe to which it is secured. In this embodiment, the first predefined signal may be a predefined rate of rise in the temperature value over two or more successive samples and the second predefined signal may be a predefined rate of drop in the temperature value over two or more successive samples. In an alternative exemplary embodiment, the sensor is a flow sensor. The output signal of the flow sensor represents the rate of flow through the outlet pipe to which it is secured. In this embodiment, the first predefined signal may be a predefined upper flow rate value. Accordingly, the second predefined signal may be a predefined lower flow rate value. The flow sensor may be any of an ultrasonic flow sensor, a piezoelectric flow sensor, and an electromagnetic flow sensor, to name but a few examples.

Figure 1 shows a system (1 00) for determining a customised heating schedule for a water heater in accordance with a first exemplary embodiment of the invention. The system includes an electrical water heater (101 ) as may be used in home or industrial applications and which has a water inlet pipe (1 03) and a water outlet pipe (105). In this embodiment, the pipes may be copper pipes. The water inlet pipe (103) receives cold water from a main water supply connection, typically a municipal water supply connection, in the direction indicated by the arrow (1 04). The water that is heated by the water heater (101 ) egresses therefrom through the water outlet pipe (105), in the direction indicated by the arrow (106), and provides heated water to hot water supply points, in the present example at a bathtub (107), a shower (109), and a tap (1 1 1 ) at a basin, through a network of hot water pipes (not shown) in fluid communication with the water outlet pipe (105).

A temperature sensor (1 13) is secured to an outer surface of the outlet pipe (105) and measures the temperature of the surface of the outlet pipe (105). The temperature sensor (1 13) may be a low-cost temperature probe and may be secured to the outlet pipe by any suitable means such as cable ties, adhesive tape, clips, or a non-adhesive shroud or wrapping, to name but a few example securing methods. It will be appreciated that this provides for a non-invasive method of securing the temperature sensor (1 1 3) to the outlet pipe (105).

The system (100) furthermore includes a control unit (1 15). The control unit (1 15) is an electronic component control box which contains additional components necessary to facilitate operation of the system. These components may include, for example, one or more digital logic devices including microprocessors, digital signal processors (DSP's), Field-programmable Gate Arrays (FPGA's), Complex Programmable Logic Devices (CPLD's), Analogue to Digital Converters (ADC's); one or more analogue components including amplifiers and filters; one or more switching components including relays, contactors and triacs; and numerous integrated and discrete active and passive supporting components. The control unit (1 15) may be configured to control the electrical energy supply (1 17) to the water heater or may be used in concert with an existing intelligent water heater system. It should be noted that the temperature of the outlet pipe (105) will rise as a result of hot water flowing through it from the water heater (101 ). Securing the temperature sensor (1 13) to the outer surface of the outlet pipe (105) greatly simplifies installation as compared to impeller type water flow meters, the installation of which is of an invasive nature and requires specialised tools and installer expertise. Measuring a rise in the temperature of the outlet pipe (105) therefore indicates that hot water is flowing from the reservoir of the water heater (101 ) and through the outlet pipe (105).

A block diagram of the control unit (1 1 5) is shown in Figure 2. The control unit includes a temperature receiving component (201 ), for receiving sample output signals from the temperature sensor (1 13); a usage event detection component (203), for detecting the start and end of hot water usage events; a memory component (205), for storing water usage events data; a usage profile updating component (207), for updating a hot water usage profile; an energy supply control component (209), for controlling the supply of electrical power to the heating element of the water heater; and a scheduling component (21 1 ) for scheduling usage times at which water in the heater should be at a desired usage temperature. These components are logical components implemented by means of hardware units and software running on digital circuits as will be apparent to those of skill in the art.

A usage profile is among the data that is stored by the memory component (205) of the system (100). In this embodiment, the memory component (205) may include a digital memory. The usage profile includes expected usage times at which water from the water heater (1 01 ) will be used and at which time the water should be at a desired usage temperature. An exemplary method whereby the expected usage times are determined will explained in greater detail below. The energy supply control component (209) may be configured to regulate the electrical energy supply to the heating element of the water heater (101 ) such that the water heater may heat its water contents to a desired usage temperature at or shortly before the times that hot water usage events are expected to occur.

During a usage event, water is drawn from the electrical water heater (101 ) through the outlet pipe (105). The outlet pipe conducts heat from the water, which results in an increase in the temperature of the outer surface of the outlet pipe, which is measured by the temperature sensor (1 13). When a usage event has ended, water stops flowing through the outlet pipe (105). Heat is then dissipated from the water that remains in the outlet pipe (105), through the pipe, to its surrounding environment. The temperature of the outer surface of the outlet pipe (105) therefore reduces as heat is dissipated, and a lower temperature is measured than during the usage event. The output signal of the temperature sensor (1 13), secured to the outlet pipe, is periodically sampled by the temperature receiving component (201 ). In this exemplary embodiment, the sampling period is once every minute. Figure 3 is a graph showing an example of sampled temperatures measured by the temperature sensor (1 13) for a single usage event versus time. The start and end times of events are determined by analysing the rate of change in the sampled temperature. In one exemplary illustration, a start event is classified as an increase of 4 degrees Celsius CO) or more over two samples. After an event has started, an end event is classified as a decrease of 2°C or more over seven samples. These values were derived empirically for an electrical water heater that was used during testing and are optimised for a one minute sampling interval and a temperature sensor with an accuracy of about 1 °C. It will be appreciated that other values also fall within the scope of the invention. For example, the use of a non-metal output pipe may also affect the heat transfer characteristics and will therefore require adaptation of the sampling period, usage start/end event criteria, and the like.

In this example, between time index 2 and time index 4 in Figure 3, there is an increase in temperature of 6°C, indicated as ΔΤ1 , which meets the criteria for a hot water usage start event. The temperatures at time index 2 and time index 3 are the same. Therefore, the usage event detection component (203) will only record time index 3 as the start of the usage event. The time for the time index is provided by the scheduling component (21 1 ) and will be recorded by the memory component (205). Between time index 6 and time index 13, there is a temperature drop of 2°C, indicated as ΔΤ2, over seven samples which meets the criteria for a usage stop event. Again, since the sampled temperature is the same at time intervals 6, 7 and 8, the usage event detection component (203) will only record time index 8 as the end of the usage event. The usage event was thus 5 minutes long. The detection of each usage event in this manner, and the recording thereof by the memory component (205), allows the control unit (1 1 5) to create a usage profile of the electrical water heater. Based on the usage profile, a customised heating schedule for the electrical water heater may be determined, and the electricity supply to the electrical water heater may be controlled to ensure that the water is at the desired usage temperature at the expected usage times, as will be elaborated on below.

Figure 4 is a graph showing an additional example of temperatures measured by the temperature sensor for two usage events occurring within a few minutes of each other. When usage events occur within a short enough time of one another, the pipe may not have cooled completely. At time index 7 in Figure 4, a first usage event occurs. The rise in temperature (ΔΤ1 ) which meets the criteria for a start event is between time index 6 and 8, with time index 7 being recorded as the start of the usage event because the temperature is the same at time index 6 and 7. Similar to the graph of Figure 4, the usage event ends at time index 12, as that is the start of the period at which cooling begins, with a 2 °C drop occurring over the seven samples between time index 10 and time index 17, and time index 12 being identified as the first sample where the temperature drops. The first usage event was thus 5 minutes long. At time index 17, and before the pipe has cooled to match the ambient temperature, a new usage event occurs. The temperature of the outlet pipe is still significantly higher than the ambient temperature at that point in time. For this usage event, the rise of 7°C occurs between time index 17 and 1 9. However, in contrast to the first usage event shown (ΔΤ2), the usage event occurs at the first time index at which the temperature increase is initiated, and not at the middle time index. The end of the second usage event of Figure 4 occurs at time index 19, which is the start of a drop in temperature of well over 2 °C between time index 1 9 and time index 26. The second usage event was thus 2 minutes long. The usage event detection component (203) detects the usage event accordingly and is recorded by the memory component (205). It should be noted that, in this embodiment, the temperature receiving component (201 ) and usage detection component (203) record rate of rise and rate of drop of the temperature sensor, and not absolute temperature. Therefore, the system (100) is able to record usage events that are in short succession and furthermore to function over a wide range of ambient temperatures, provided that the ambient temperature does not approach or exceed the temperature of the outlet pipe, which is typically above 50 °C.

Figure 5 shows a flow diagram illustrating an exemplary method (500) to detect and record a usage event. It should be noted that the method illustrated in the flow diagram is repeated for every time index at which the temperature of the outlet pipe (105) is sampled, which in the described embodiment is once per minute. The information that is scrutinised by the usage event detection component (203) is contingent on whether a usage event is underway at present. If it is determined (501 ) that no event is underway at that point in time, the method (500) attempts to find a start event. The outlet pipe (105) temperature value is received (503) from the temperature sensor, in the form of an output signal thereof, by the temperature receiving component (201 ) and compared with the previous two received sample values. If (505) the increase is less than the amount required to signify a start event, the method restarts at the next time index. If the increase in temperature is more than the required 4°C, a start event is identified by the usage event detection component (203). The start time index is then determined (507) by the scheduling component (21 1 ), and recorded by the memory component (205), so as to store the start time of the usage event. As explained with reference to Figures 3 and 4, the start time will typically be the time index immediately before an initial increase in temperature value was detected. Once an event has started, the method attempts to identify an end event. The temperature reading is sampled, in this exemplary embodiment once per minute, by the temperature receiving component (201 ) and compared (509) with the previous seven temperature samples. If a decrease in temperature is determined (51 1 ) of not more than the required 2°C over seven readings or less, the method resumes attempting to find an end event after measuring the temperature at a next time period. If the decrease in temperature is more than 2 °C, an end event is determined to have occurred. The difference in time between the start event and the end event is then determined (513) by the scheduling component (21 1 ), and is recorded as the duration of the usage event by the memory component (205). It should be noted that a usage event will typically be discarded if continues beyond a predetermined period of time, in the present embodiment more than 15 minutes. If it is determined (515) that the event duration is more than the maximum allowed period, the event is ignored (517) and discarded, and is not taken into account. If it is shorter than the maximum period, the event is stored by the memory component (205). This may avoid outlying values from influencing the user profile. After an event has been stored or discarded, the method is repeated and attempts to find a next start event.

The usage event start periods and their duration, when stored by the memory component (205), are used by the usage profile updating component (207) to update the user profile that was previously stored by the memory component (205) and are used by the scheduling component (21 1 ) to determine a customised heating schedule for the electrical water heater. By incorporating usage events as they occur, the expected usage times provided by the usage profile can be continually updated so that the energy supply control component (209) can provide electrical energy to the water heater (1 01 ) such that the heater can heat the water to a desired usage temperature at the expected usage times.

In the present example, the usage temperature is a range, which allows the water heater to turn on for a fixed period of time such that the temperature is allowed to rise to approximately the upper end of the range before the expected usage times. According to the method, the water heater can be switched off prior to the start of each expected usage time if the water has reached the usage temperature. This will result in a reduction in electrical energy usage as compared to a conventional water heater in which a thermostat energises an electrical element of the water heater whenever the temperature in the water heater drops below a predefined temperature, since standing losses are higher for warm water than for colder water.

Control of electrical energy supply to the water heater (101 ) is continuously performed by the energy supply control component (209). The scheduling component (21 1 ) determines the customised heating schedule for the electrical water heater (101 ). A predetermined time before an expected usage event is to occur, the energy supply control component (209) energises the heating element of the water heater (101 ), which allows the water heater (101 ) to heat water contained in its reservoir. The predetermined time is chosen such that water of an average temperature within the water heater can be heated so as to reach a desired usage temperature at or shortly before an expected usage event.

The temperature receiving component (201 ) periodically receives temperature readings from the temperature sensor (1 13) attached to the outlet pipe (105) as was described with reference to Figures 3 to 5. When the usage event detection component (203) detects an actual usage event with a beginning and end time, it logs the event by means of the memory component (205). The log of events can be used by the system (100) to select an appropriate customised heating schedule, such that heating stops before each predicted usage event. This method is superior to maintaining the temperature of the water heater at all times, since the temperature of the water in the water heater will be lower after the event, and standing losses are less for a tank with water at a lower temperature.

It will be appreciated that the system may merely observe hot water usage for an initial time period after installation in order to obtain sufficient historical data to determine a usage profile. In one embodiment, this observation period may be 4 weeks. Thereafter, and subsequent to determining the usage profile, the system may enter an active mode wherein it actively controls the water heater. In one embodiment, the scheduling component (21 1 ) determines a customised schedule for every day of the week, as usage patterns may be different on, for example, week days and weekends. In order to do so, it may retrieve, by means of the memory component (205), historical data for this specific day of the week dating back a number of weeks, such as four weeks. This historical data may include the time of day of usage events and their duration. The scheduling component (21 1 ) then determines the expected hot water events for the particular day of the week by calculating an average distribution of hot water events for that day of the week based on the previous usage events. Using these determined expected hot water events distribution, the scheduling component (21 1 ) then determines a customised heating schedule so that sufficient energy will be stored in the water heater to supply, at the expected hot water events of that particular day of the week, hot water at a desired usage temperature. This process may be repeated for each day of the week.

It will be appreciated that this provides for a windowed average, as data predating the preceding four weeks will not be included in the calculations. This will allow the system to adjust to changes in usage patterns, for example as seasons change. The window breadth need not be four weeks, but may be adjusted as the particular installation may require.

Experimental results

A conventional water meter was installed on a water inlet pipe of an electrical water heater to determine actual warm water consumption events so as to obtain a control dataset. The water meter generates an output pulse for every 0.5 litres of water used and requires a flow of more than 2 litres per minute to generate any output signals. The total number of pulses generated in a sampling interval of a minute was reported to a remote server.

Using the data obtained from the conventional water meter, the start of a water usage event was classified as a non-zero value detected after at least two zero values. The end of a water usage event was classified as two consecutive zero values following the start of an event. Two consecutive water usage events, that occur sufficiently close to one another, was considered as a single usage event.

The water usage events registered by the conventional water meter were compared to the events detected by the system of the present disclosure, to determine the accuracy of the system in terms of detecting events and estimating their duration. The event detection algorithm was tested on 49 days of outlet temperature and water meter data sampled at a frequency of once per minute, from a 150 litre electrical water heater with a 3 kW element installed in a residential household. Water usage events were classified into three categories according to the volume of warm water used: small events, which were less than 15 litres (10 percent of the electric water heater tank volume); medium events, which between 15 and 30 litres (between 10 and 20 percent of the electric water heater tank volume); and large events, which were greater than 30 litres (more than 20 percent of the electric water heater tank volume). The results are shown in the table below:

Table 1: Comparison of Method and System of the Invention to Water Meter Results

The results show that the method of the invention was able to detect 91% of usage events successfully. Of the 7 events that were not detected by the algorithm, 6 of these were small usage events where less than 2.5 litres of water was used. These events were too small to cause a large enough increase in the outlet temperature and, hence, were not detected. The large event that was missed by the system was an event that occurred 7 minutes after another large water usage event and the temperature of the outlet had not decayed sufficiently after the first event, which meant the increase in outlet temperature was below the detection threshold of 4°C. However, the system was able to correctly detect two large usage events that occur within 10 minutes of one another.

False positives are events indicated by the system where no warm water usage was registered by the water meter. Five such events were detected and may have been caused by one of two possible scenarios: a low flow rate warm water draw that causes hot water to flow through the outlet pipe but below the minimum flow rate required by the water meter (i.e. 2 litres per minute), or low volume usage events that are less than the minimum volume of water that would cause the water meter to generate a pulse (i.e. 0.5 litres per pulse).

Figure 6 shows a system (600) for determining a customised heating schedule for a water heater in accordance with a further exemplary embodiment of the invention. The system includes an electrical water heater (601 ) as may be used in home or industrial applications and which has a water inlet pipe (603) and a water outlet pipe (605). The water inlet pipe (603) receives cold water from a main water supply connection, typically a municipal water supply connection, in the direction indicated by the arrow (604). The water that is heated by the water heater (601 ) egresses therefrom through the water outlet pipe (605), in the direction indicated by the arrow (606), and provides heated water to hot water supply points, in the present example at a bathtub (607), a shower (609), and a tap (61 1 ) at a basin, through a network of hot water pipes (not shown) in fluid communication with the water outlet pipe (605).

A flow sensor (613) is secured to an outer surface of the outlet pipe (605) and is able to measure the flow rate of water flowing through the outlet pipe (605). The flow sensor (613) is an externally installed, non-invasive flow sensor and may be secured to the outlet pipe by any suitable means such as cable ties, adhesive tape, clips, or a non-adhesive shroud or wrapping, to name but a few example securing methods. The flow sensor (613) may operate by means of ultrasonic and electromagnetic flow sensing, to name two exemplary flow sensing methods. The system (600) furthermore includes an electronic control unit (615) with similar components to that of the control unit in the first exemplary embodiment.

It should be noted that the measured flow in the outlet pipe (605) will increase as a result of hot water flowing through it from the water heater (601 ). Securing the flow sensor (613) externally onto the outlet pipe (605) greatly simplifies installation as compared to impeller type water flow meters, the installation of which, as mentioned above, is of an invasive nature and requires specialised tools and installer expertise. Measuring a flow rate above a certain upper threshold in the outlet pipe (605) therefore indicates that hot water is flowing from the reservoir of the water heater (601 ) and through the outlet pipe (605). Similarly, measuring a flow rate below a certain lower threshold in the outlet pipe (605) indicates that hot water is not flowing through the outlet pipe (605) or that the flow is negligible.

A block diagram of the control unit (615) is shown in Figure 7. The control unit includes a flow rate receiving component (701 ), for receiving sample output signals from the flow sensor (613); a usage event detection component (703), for detecting the start and end of hot water usage events; a memory component (705), for storing water usage events data; a usage profile updating component (707), for updating a hot water usage profile; an energy supply control component (709), for controlling the supply of electrical power to the heating element of the water heater; and a scheduling component (71 1 ) for scheduling usage times at which water in the heater should be at a desired usage temperature. These components are logical components implemented by means of hardware units and software running on digital circuits as will be apparent to those of skill in the art.

A usage profile is among the data that is stored by the memory component (705) by the system (600). In this embodiment, the memory component (705) may include a digital memory. The usage profile includes expected usage times at which water from the water heater (701 ) will be used and at which time the water should be at a desired usage temperature. An exemplary method whereby the expected usage times are determined in this exemplary embodiment will explained in greater detail below.

The energy supply control component (709) may be configured regulate the electrical energy supply to the heating element of the water heater (601 ) such that the water heater may heat its water contents to a desired usage temperature at or shortly before the times that hot water usage events are expected to occur.

During a usage event, water is drawn from the electrical water heater (601 ) through the outlet pipe (605) the flow rate of which is measured by the flow sensor (613). When a usage event has ended, water stops flowing through the outlet pipe (605). The output signal of the flow sensor (613), secured to the outlet pipe, is periodically sampled by the flow rate receiving component (701 ). In this exemplary embodiment, the sampling period is once every minute. Figure 8 is a graph showing an example of sampled flow rates measured by the flow sensor (613) for a single usage event versus time. The start and end times of hot water usage events are determined by analysing the sampled flow rates. In one exemplary illustration, a start event is classified when a flow rate is measured exceeding an upper threshold, indicated in Figure 8 as F(upper) and sustaining a flow exceeding F(upper) for at least two samples. After an event has started, a stop event is classified when measuring a flow rate below a lower threshold, indicated in Figure 8 as F(lower) and sustaining a flow rate below F(lower) for at least two samples. It will be appreciated that other values, such as differing sampling periods, also fall within the scope of the invention. A certain installation may require a sustained flow exceeding the upper threshold for a different number of consecutive samples to classify a start event and, similarly, to sustain a flow below the lower threshold for a different number of samples to classify an end event.

In this example, between time index 2 and time index 3 in Figure 8, there is an increase in flow rate exceeding F(upper). However, at time index 4, the flow rate falls below F(upper). Therefore, a start event is not classified, as a flow rate exceeding F(upper) was not sustained for at least 2 consecutive sample periods.

At time index 5, the flow once again exceeds F(upper) and sustains a flow rate exceeding F(upper). At time index 7, the usage event detection component (703) identifies a usage event start since a flow rate exceeding F(upper) had been sustained for at least 2 consecutive sample periods. Time index 5 will be identified as the starting time, as it is the first sample value to exceed F(upper) during this exemplary usage event start. At time index 9, the flow rate drops below F(lower), but exceeds F(lower) at time index 10. An end event is therefore not classified as a flow rate below F(lower) had not been sustained for at least 2 sample periods. At time index 1 1 , the flow rate again drops below F(lower). At time index 13, the usage event detection component (703) identifies a usage event end since a flow rate below F(lower) had been sustained for at least 2 consecutive sample periods. Time index 1 1 will be identified as the end time, as it is the first sample value below F(lower) during this exemplary usage event stop. The usage event started at time index 5 and ended at time index 1 1 . This exemplary usage event therefore continued for 6 minutes. The time for each of the time indices above is provided by the scheduling component (71 1 ) and will be recorded by the memory component (705).

The detection of each usage event in this manner, and the recording thereof by the memory component (705), allows the control unit (615) to create a usage profile of the electrical water heater. Based on the usage profile, a customised heating schedule for the electrical water heater can be determined, and the electricity supply to the electrical water heater can be controlled to ensure that the water is at the desired usage temperature at the expected usage times, as will be elaborated on below. Figure 9 shows a flow diagram illustrating an exemplary method (900) to detect and record a usage event for subsequent use in determining a customised heating schedule. It should be noted that the method illustrated in the flow diagram is repeated for every time index at which the flow rate through the outlet pipe is sampled, which in the described embodiment is once per minute. The information that is scrutinised by the usage event detection component (703) is contingent on whether a usage event is underway at present.

If it is determined (901 ) that no event is underway at that point in time, the method attempts to find a start event. The outlet pipe (605) flow rate value is received (903) from the flow sensor, in the form of an output signal thereof, by the flow rate receiving component (701 ) and compared to the previous two received values. If the flow rate is below the threshold required to signify a start event, the method restarts at the next time index. If the flow rate exceeds the upper flow threshold, a start event is identified by the usage event detection component (703). The start time index is then determined (907) by the scheduling component (71 1 ), and recorded by the memory component (705), so as to store the start time of the usage event.

Once an event has started, the method attempts to identify an end event. The flow rate is sampled, in this exemplary embodiment once per minute, and received (909) by the flow rate receiving component whereafter the sample value is compared the previously received sample values. If (91 1 ) the flow rate is not below the lower threshold, the method resumes attempting to find an end event after measuring the flow rate at a next time period. If, however, the flow rate falls below the lower threshold, an end event is determined to have occurred. The difference in time between the start event and the end event is then determined (913) by the scheduling component (71 1 ), and is recorded as the duration of the usage event by the memory component (705).

It should be noted that a usage event will typically be discarded if it continues beyond a predetermined period of time, in the present embodiment more than 15 minutes. If it is determined (915) that the event duration is more than the maximum allowed period, the event is ignored (917) and discarded, and is not taken into account. If it is shorter than the maximum period, the event is stored by the memory component (705). This may avoid outlying values from influencing the user profile. After an event has been stored or discarded, the method is repeated and attempts to find a next start event. The usage event start periods and their duration, when stored by the memory component (705), are used by the usage profile updating component (707) to update the user profile and are used by the scheduling component (71 1 ) to determine a customised heating schedule for the electrical water heater. By incorporating usage events as they occur, the expected usage times provided by the usage profile can be continually updated so that the energy supply control component (709) can provide electrical energy to the water heater (601 ) such that the heater can heat the water to a desired usage temperature at the expected usage times.

Control of electrical energy supply to the water heater (601 ) is continuously performed by the energy supply control component (709). The scheduling component (71 1 ) determines the customised heating schedule for the electrical water heater (601 ). A predetermined time before an expected usage event is to occur, the energy supply control component (709) starts providing electrical energy to the water heater (601 ), which allows the water heater to heat water in its reservoir. The predetermined time is chosen such that water of an average temperature within the water heater can be heated so as to reach a desired usage temperature at or shortly before an expected usage event.

An alternative embodiment is envisaged wherein the flow sensor is replaced with a vibration sensor. In such an embodiment, the vibration amplitude of the outlet pipe of the water heater is measured. When hot water is drawn from the water heater, the turbulence of the water flowing through the pipe will cause the pipe to vibrate. These vibrations may be detected by means of a vibration sensor secured to the outlet pipe. This vibration sensor may be a passive vibration sensor, a Microelectromechanical systems (MEMS) accelerometer, piezoelectric sensors and the like as will be apparent to those skilled in the art. In an even further alternative embodiment, it is envisaged that an electromagnetic flow meter may be utilised. This embodiment will operate similarly to the previously described embodiment wherein a flow sensor is used, with the required modifications so as to measure and evaluate the relevant sensor output signals to determine the start and end of hot water usage events.

It will be appreciated by those skilled in the art that the embodiments disclosed herein may contribute to a reduction in electrical energy usage by ensuring that a water heater is only activated at required times. By updating a user profile on a regular basis, such as once per day, thereby altering the expected usage times, the system may adapt to changes in a user's usage patterns, for example during seasonal changes when a user may use hot water at continuously changing times. The customised heating schedule is thus updated based on actual usage patterns. The usage profile may also provide expected usage times for different days of the week, recorded by the scheduling component. This may compensate for a user typically using hot water later in the mornings over weekends compared to weekdays, where a user may need to use water earlier before going to work.

Additionally, relatively isolated events occurring at specific days may be compensated for. If, for example, a user has a housekeeper who visits their home on a specific day, and the housekeeper uses hot water at a specific time during the day. In this case, the usage profile may be updated to account for changes in the measured time and duration of hot water events for a specific day of the week, and the usage event for that day of the week used to determine the customised heating schedule. In that case, the customised heating schedule will only be updated once per week, to account for the measured usage on specific days in the previous week.

It will furthermore be appreciated that the system may be retrofitted to existing water heaters easily and inexpensively by securing the relevant sensor to an outer surface of the outlet pipe of the water heater. The use of expensive impeller-type water flow meters, which are difficult to install and may require plumping pipes to be cut as part of the installation of such meters, is thereby avoided. Since the installation of the present disclosure is non-invasive and does therefore not require any adaptation of existing plumbing, the installation does not require the installer to have any plumbing expertise.

The invention is furthermore not limited to electrical water heaters but could also be used with any other kind of water heaters such as gas heaters, for example.

Throughout the specification and claims unless the contents requires otherwise the word 'comprise' or variations such as 'comprises' or 'comprising' will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.