HOT WATER POWER CONTROLLER

Field of the invention

The present invention relates to a hot water power control system and in particular, but not exclusively, to a system for managing and controlling water temperature in a water storage unit.

Background to the invention

Devices for storing hot water, such as domestic hot water cylinders, are often controlled by a thermostat including bimetallic strip type thermostats. Such thermostats generally provide poor temperature control accuracy and temperature differences between thermostats may vary up to several degrees. Such thermostats also do not allow the water temperature to be lowered below their set temperature.

Further, hot water storage units often have a cycle initiated to address leglonella growth concerns. Such cycles periodically heat the water to a temperature where legionella growth is subdued or annihilated. However, such cycles are often initiated at times that are inefficient.

It is an object of the present invention to provide a way of controlling temperature that which improves or at least ameliorates some of the abovementioned disadvantages or which at least provides the public with a useful choice. Other objects of the invention may become apparent from the following description which is given by way of example only.

In this specification, where reference has been made to external sources of information, including patent specifications and other documents, this is generally for the purpose of providing a context for discussing the features of the present invention. Unless stated otherwise, reference to such sources of information is not to be construed, in any jurisdiction, as an admission that such sources of information are prior art or form part of the common general knowledge in the art.

Summary of the invention

Accordingly, in a first aspect the present invention relates to a system for controlling a heater adapted to heat water in a water storage unit comprising a control apparatus adapted for connection to a sensor adapted to measure temperature of the water in the water storage unit and wherein the control apparatus is configured to: receive the temperature measurement from the sensor, store a value indicative of a desired temperature, compare the temperature measurement to the desired temperature, output a signal operable to energise the heater when temperature measurement is below a combination of the desired temperature and a tolerance temperature, and wherein the tolerance temperature is a value based on whether the water storage unit experiences, or is predicted to experience, high or low water usage.

In another aspect the invention broadly consists in a system for controlling a heater adapted to heat water in a water storage unit comprising one or more sensors adapted to output one or more signals indicative of the temperature of the water in the water storage unit and a control apparatus, wherein the control apparatus is configured to: receive the one or more signals indicative of the temperature of the water in the water storage unit, store a value indicative of a desired temperature of the water in the water storage unit, compare the one or more signals indicative of the temperature of the water in the water storage unit to the value indicative of the desired temperature of the water in the water storage unit, output a signal operable to energise the heater when at least one of the one or more signals indicative of the temperature of the water in the water storage unit is below a combination of the value indicative of the desired temperature and a value indicative of a tolerance temperature, and wherein the tolerance temperature is a value based on whether the water storage unit experiences, or is predicted to experience, high or low water usage.

Preferably high water usage is determined by the temperature of water in the water storage unit dropping below the desired temperature by a threshold value.

Preferably control apparatus is further configured to the compare the one or more signals indicative of the temperature the water in the water storage unit to a value indicative of a desired temperature of the water in the water storage unit and store data, for each of a first plurality of time period parameters, representing :

i. a determination of high water usage based on the desired temperature being greater than a measure of the temperature the water in the water storage unit by a threshold value, and

ii. a determination of low water usage based on the desired temperature being less than the measure of the temperature the water in the water storage unit by the threshold value.

Preferably the threshold value is a value indicative of 10°C. Preferably the first plurality of time period parameters each represents a period of one hour for each hour of day of a seven day cycle.

Preferably the measure of the temperature the water in the water storage unit is a value indicative of the average water temperature in the water storage unit for each of the first plurality of time period parameters.

Preferably the tolerance temperature is 5°C below the desired temperature for a time period parameter with the determination of a high water usage.

Preferably the tolerance temperature is 6°C below the desired temperature for a time period parameter with the determination of a low water usage.

Preferably the desired temperature is a temperature is less than 60°C.

Preferably the desired temperature is a temperature between 40°C to 60°C.

Preferably the control apparatus is further configured to calculate a value indicative of the average temperature in the water storage unit for each of a second plurality of time period parameters.

Preferably each of the second plurality of time period parameters represents a period of one day for each day of a seven day cycle.

Preferably the control apparatus is further configured to output a signal operable to energise the heater, when the value indicative of the average temperature is comparable to a threshold temperature and a threshold time period has elapsed, such that the one or more temperature sensors outputs a signal indicative of the temperature of the water in the water storage unit is at least 60°C.

Preferably the threshold time period is dependent upon the average temperature.

Preferably the threshold time period increases as the average temperature increases. Preferably the threshold time period increases exponentially as the average temperature increases.

Preferably the threshold time period decreases as the average temperature decreases.

Preferably the threshold time period decreases exponentially as the average temperature decreases.

Preferably the threshold is approximately three days when the accumulative average temperature is less than 40°C. Preferably the threshold is approximately five days when the accumulative average temperature is at least 40°C. Preferably the threshold is approximately nine days when the accumulative average temperature is at least 45°C.

Preferably the threshold is approximately thirteen days when the accumulative average temperature is at least 50°C.

Preferably the threshold is approximately twenty one days when the accumulative average temperature is at least 55°C.

Preferably the temperature is controlled with a variable hysteresis range, wherein the range for high historical usage is lower than the range for low historical usage.

In another aspect the invention broadly consists in a method of controlling a heater adapted to heat water in water storage system that comprises a water storage unit, one or more sensors adapted to output one or more signals indicative of the temperature of the water in the water storage unit and a control apparatus, wherein the control apparatus is configured perform the steps of:

receiving the one or more signals indicative of the temperature of the water in the water storage unit,

storing a value indicative of a desired temperature of the water in the water storage unit,

comparing the one or more signals indicative of the temperature of the water in the water storage unit to the value indicative of the desired temperature of the water in the water storage unit, and

outputting a signal operable to energise the heater when at least one of the one or more signals indicative of the temperature of the water in the water storage unit is below a combination of the value indicative of the desired temperature and a value indicative of a tolerance temperature wherein the tolerance temperature is a value based on whether the water storage unit experiences, or Is predicted to experience, high or low water usage.

In another aspect the invention broadly consists in a system operable to initiate a bacteria killing cycle in a water storage unit whereby water in the water storage unit is heated to at least 60°C, the system comprising one or more sensors adapted to output one or more signals indicative of the temperature of the water in the water storage unit, a heater adapted to heat the water in the water storage unit and a control apparatus, wherein the control apparatus is configured to:

receive the one or more signals indicative of the temperature the water in the water storage unit,

store data representative of:

• an average temperature of the water in the water storage unit over a time period since a last bacteria killing cycle,

• a plurality of average temperatures and/or plurality of ranges of

average temperatures, and

• a plurality of bacteria killing cycle delay times each associated with the average temperature and/or range of average temperatures, wherein the controller is configured to output a signal to initiate the bacteria killing cycle when the time period since the last bacteria killing cycle equals or exceeds the cycle delay time associated with the average temperature.

In another aspect the invention broadly consists in a system for use with a water storage unit that heats water, the system operable to initiate a bacteria killing cycle in a water storage unit, the system comprising:

a controller with a control output for connection to and control of a water heater in a water storage unit, and one or more inputs for receiving signals indicative of the temperature in a water storage unit to which it is connected, and

optionally, one or more sensors connected to or for connection to the inputs and for sensing temperature of and outputting signals indicative of the temperature in a water storage unit,

wherein the controller is configured to:

determine an average temperature of water in a water storage unit over a time period from signals on the one or more inputs,

determine a bacteria killing cycle time correlating to the average temperature, and

initiate the bacteria killing cycle when the time elapsed since the last bacteria killing cycle correlates to (e.g. equals or exceeds) the determined bacteria killing cycle time. In another aspect the invention broadly consists in a system operable to initiate a bacteria killing cycle in a water storage unit whereby water in the water storage unit is heated to at least 60°C, the system comprising one or more sensors adapted to output one or more signals indicative of the temperature of the water in the water storage unit, a heater adapted to heat the water in the water storage unit and a control apparatus, wherein the control apparatus is configured to:

receive the one or more signals indicative of the temperature the water in the water storage unit,

store data representative of:

• an average temperature of the water in the water storage unit over a time period since a last bacteria killing cycle,

wherein the control apparatus is configured to initiate the bacteria killing cycle after a time period that non linearly or exponentially increases with decreased average temperature.

Preferably the controller correlates each of a plurality of average temperatures (or ranges of average temperatures) to different respective bacteria killing cycle times, and the controller is configured to determine the bacteria killing cycle time by determining the respective bacteria killing cycle time that correlates to the average temperature of the water in the water storage unit.

Preferably the controller correlates each of a plurality of average temperatures (or ranges of average temperatures) to respective bacteria killing cycle times by:

associating each average temperature (or range of average temperatures) with different respective bacteria killing cycle times in a look up table, and/or

associating each average temperatures (or range of average temperatures) with respective bacteria killing cycle times by a mathematical or empirical relationship. Preferably the control apparatus is configured to initiate the bacteria killing cycle after a time period that non linearly or exponentially increases with decreased average temperature.

Preferably data representative of the average temperature is updated every six minutes.

Preferably a delay time is approximately three days when the average temperature is less than 40°C.

Preferably a delay time is approximately five days when the average temperature is approximately 40°C to 45°C.

Preferably a delay time is approximately nine days when the average temperature is approximately 45°C to 50°C. Preferably a delay time is approximately thirteen days when the average temperature is approximately 50°C to 55°C.

Preferably a delay time is approximately twenty one days when the average temperature is approximately 55°C to 60°C.

In another aspect the invention broadly consists in a system operable to initiate a bacteria killing cycle in a water storage unit whereby water in the water storage unit is heated to at least 60°C, the system comprising one or more sensors adapted to output one or more signals indicative of the temperature of the water in the water storage unit, a heater adapted to heat the water in the water storage unit and a control apparatus, wherein the control apparatus is configured to:

receive the one or more signals indicative of the temperature the water in the water storage unit,

store data representative of:

• an average temperature of the water in the water storage unit over a time period since a last bacteria killing cycle,

• a plurality of average temperatures and/or plurality of ranges of

average temperatures, and

· a plurality of bacteria killing cycle delay times each associated with the average temperature and/or range of average temperatures, compare the one or more signals indicative of the temperature the water in the water storage unit to a value indicative of a desired temperature of the water in the water storage unit and store data, for each of a first plurality of time period parameters, representing:

i. a determination of high water usage based on the desired temperature being greater than a measure of the temperature the water in the water storage unit by a threshold value, and

ii. a determination of low water usage based on the desired temperature being less than the measure of the temperature the water in the water storage unit by the threshold value,

wherein the controller is configured to output a signal to initiate the bacteria killing cycle when the time period since the last bacteria killing cycle equals or exceeds the cycle delay time associated with the average temperature, and the time is determined to be a time period of low water usage.

Preferably the threshold value is a value indicative of 10°C.

Preferably the time period parameter is a period of one hour. Preferably the controller is configured to output a signal to initiate the bacteria killing cycle upon the elapse of twenty three hours if there is not a time period parameter determined to one of a low water usage within the next twenty three hours.

In another aspect the invention broadly consists in a system operable to initiate a bacteria killing cycle whereby water in a water storage unit is heated to at least 60°C after a period of time, and the water is otherwise controlled to a temperature that is lower than 60°C, wherein the period of time is dependent on the average temperature of the water during the period of time.

In another aspect the invention broadly consists in a method of initiating a bacteria killing cycle for a water storage system whereby water in a water storage unit is heated to at least 60°C, the system comprising one or more sensors adapted to output one or more signals indicative of the temperature of the water in the water storage unit, a heater adapted to heat the water in the water storage unit and a control apparatus, wherein the control apparatus is configured perform the steps of:

receiving the one or more signals indicative of the temperature the water in the water storage unit,

storing data representative of:

• an average temperature of the water in the water storage unit over a time period since a last bacteria killing cycle,

• a plurality of average temperatures and/or plurality of ranges of

average temperatures, and

· a plurality of bacteria killing cycle delay times each associated with the average temperature and/or range of average temperatures, wherein the controller is configured to output a signal to initiate the bacteria killing cycle when the time period since the last bacteria killing cycle equals or exceeds the cycle delay time associated with the average temperature.

In another aspect the invention broadly consists in a method of initiating a bacteria killing cycle for a water storage system whereby water in a water storage unit is heated to at least 60°C, the system comprising one or more sensors adapted to output one or more signals indicative of the temperature of the water in the water storage unit, a heater adapted to heat the water in the water storage unit and a control apparatus, wherein the control apparatus is configured perform the steps of:

receiving the one or more signals indicative of the temperature the water in the water storage unit,

storing data representative of: • an average temperature of the water in the water storage unit over a time period since a last bacteria killing cycle,

• a plurality of average temperatures and/or plurality of ranges of

average temperatures, and

· a plurality of bacteria killing cycle delay times each associated with the average temperature and/or range of average temperatures, comparing the one or more signals indicative of the temperature the water in the water storage unit to a value indicative of a desired temperature of the water in the water storage unit and store data, for each of a first plurality of time period parameters, representing :

iii. a determination of high water usage based on the desired temperature being greater than a measure of the temperature the water in the water storage unit by a threshold value, and

iv. a determination of low water usage based on the desired temperature being less than the measure of the temperature the water in the water storage unit by the threshold value,

wherein the controller is configured to output a signal to initiate the bacteria killing cycle when the time period since the last bacteria killing cycle equals or exceeds the cycle delay time associated with the average temperature, and the time is

determined to be a time period of low water usage.

Preferably the desired temperature is in the range of 30°C to 60°C, 35°C to 60°C, 40°C to 60°C, 45°C to 60°C, 50°C to 60°C or 55°C to 60°C, 30°C to 55°C, 30°C to 50°C, 30°C to 45°C, 30°C to 40°C, 30°C to 35°C, 30°C to 35°C, 35°C to 40°C, 40°C to 45°C, 45°C to 50°C, 50°C to 55°C, 55°C to 60°C, 40°C to 60°C or 40°C to 45°C.

In another aspect the invention relates to any one or more of the above statements in combination with any one or more of any of the other statements.

Other aspects of the invention may become apparent from the following description which is given by way of example only and with reference to the accompanying drawings.

As used herein the term "and/or" means "and" or "or", or both. The term "comprising" as used in this specification and claims means "consisting at least in part of". When interpreting statements in this specification and claims which include that term, the features, prefaced by that term in each statement, all need to be present but other features can also be present. Related terms such as "comprise" and

"comprised" are to be interpreted in the same manner. It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7).

The entire disclosures of all applications, patents and publications, cited above and below, if any, are hereby incorporated by reference. This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

Brief description of the drawings

The invention will now be described by way of example only and with reference to the drawings in which:

Figure 1 shows a schematic of a system according to particular embodiments of the invention.

Figure 2 shows an example embodiment of the system where a domestic hot water cylinder has a temperature sensor adapted to provide a signal indicative of the temperature of the cylinder to a controller.

Figure 3 illustrates an arrangement for temperature sensing. Figure 4 illustrates a flow diagram of the steps undertaken by the controller used for determining whether high or low water usage occurs for each one of a plurality of the time period parameters.

Figure 5 illustrates a flow diagram of the steps undertaken by the controller used for processing water usage statistics on a daily basis. Figure 6 illustrates a flow diagram of steps undertaken by the controller to control general heating operation of the hot water storage tank in accordance with some embodiments. Figure 7 shows a graph of ideal time periods that elapse for an accumulative average temperature of the water in the water storage tank before the bacteria killing cycle is initiated.

Figure 8 illustrates flow diagrams outlining detailed processes undertaken by the controller in accordance with to particular embodiments.

Figure 9 shows an example of logged temperature of the water stored in a water storage unit controlled in accordance with some embodiments of the invention.

Figure 10 shows a bar graph of system energy use performance of the controller of the prior art based on the water usage and temperature. Figure 11 shows a bar graph of the same data controlled in accordance with some embodiments of the invention.

Detailed description of the invention

The invention relates to controlling the temperature of water in a hot water storage device. It is desirable to select a particular temperature of the water below 60°C for reasons including mitigating the risk of injury by burning and/or reducing energy consumption. However, lowering the temperature of water below 60°C generates a health risk in that bacteria, such as legionella, is able to grow. Further, lowering the

temperature of water in a hot water storage device poses a risk of running out of hot water entirely, particularly in limited supply domestic environments. Particular embodiments herein described relate to a system that enables an energy saving potential and/or greater safety through lowering the temperature of when compared to systems of the prior art, yet mitigates the risk of running out of hot water. In these embodiments the system provides control of the water in a storage unit by allowing the water temperature to be lowered. The lowering of the temperature saves energy that would otherwise have been used to heat the water to a higher temperature. The lowering of the water temperature also provides improved safety by enabling water temperatures incapable of burning.

Lowering of the water temperature (to obtain improved use of energy or safety advantages) is generally achieved by controlling the temperature of water to a particular target temperature below 60°C, for example, 45°C. The target temperature also has a tolerance temperature range below the target temperature that the temperature of the water in a storage unit is allowed to fall to. The particular tolerance temperature is a value based on whether the water storage unit experiences, or is predicted to

experience, high or low water usage. High water usage is determined by the temperature of water in the water storage unit dropping below the desired temperature by a threshold value. For example, the controller can make a determination of high water usage when temperature of water in the storage unit drops below the desired temperature by a threshold value. The threshold value can be when, for example, the temperature of the water in the water storage unit drops by 10°C below a desired temperature. A temperature reading can be made around every hour. Multiple temperature readings can be statistically treated or combined to determine a useful representative measure of the water temperature over the previous hour. For example, the measure could be an average or median, maximum or minimum value. The tolerance temperature can be 5°C below the desired temperature for a time period parameter with the determination of high water usage, and lower, such as 6°C below the desired temperature for a time period parameter with the determination of low water usage. This is because particular hours of the day are determined to be those where low amounts of hot water is used the temperature of the hot water in the storage unit can be allowed to drop further below the desired temperature. Energy can be saved by not immediately heating the water and because there is a low risk of hot water running out. During particular hours of the day determined to be those where high amounts hot water is used the temperature of water in the storage unit is kept closer to the desired temperature such that the risk of running out of hot water is reduced. To protect against bacteria growth in a water storage unit the water temperature must be held above 60°C or at least periodically heated to at least 60°C, known as a biocycle. Other particular embodiments herein described relate to a system that protects against bacteria whilst allowing potential energy savings and/or safety to be achieved. These embodiments allow a temperature of less than 60°C to be maintained in a hot water storage unit while also determining the most economical time to heat the water to above 60°C. The most economical time is determined by having a range of average

temperatures each associated with a time between biocycles. A biocycle is initiated when an amount of time elapses since a previous biocycle corresponds or correlates to (e.g. equals or exceeds) the time between biocycles associated with a particular average temperature in the range of average temperatures. Generally, the closer the average water temperature is to 60°C, the longer the time period between biocycles. The relationship between the elapsed time and the particular average temperature is generally nonlinear in that the further from 60°C the average water temperature is, the increasingly less time between biocycles can elapse to ensure safety. Figure 1 shows a schematic of a system 10 that accords to an embodiment of the invention. Particular components of the system 10 comprise a controller 6, a temperature sensor 7 and a switch 4. The controller can be a microprocessor having at least as many inputs and outputs as is required to interface with sensors and other components of the system 10, and is capable of storing and implementing control decisions.

The system 10 may further comprise an insulated hot water storage unit and plumbing attachments to thereby comprising a set of components that is connectable to a power source and a water source and operable to provide temperature controlled hot water. The system 10 can be optionally integrated with existing components on a premise to control the temperature water in a hot water storage unit Alternatively, the system provides all the required components for connecting to a power source and a water source and providing and temperature controlled hot water. Herein, reference to temperature readings, desired, sensed or measured temperatures are to be understood to refer to signals or stored values indicative of those referred to. The temperature sensor 7 is configured to measure the temperature of water within a hot water storage unit 1. The temperature sensor can optionally be inside the unit 1.

Alternatively, the temperature sensor is attached to the exterior of the unit. Optionally, there is more than one temperature sensor configured to sense temperature of the water in the unit 1 in multiple locations. Sensing at multiple locations within the unit is beneficial for large volumes of water where a temperature gradient over that volume may exist. Where a large volume is to be used, the controller may read temperatures in many locations and statistically treat those readings. Statistical treatment includes any one or more of taking an average value, a median value, or taking a maximum or minimum reading.

The hot water storage unit 1 has an element 2 configured to heat water within the unit 1. In some embodiments the element 2 is contained within the unit 1 while in other embodiments the element is provided external to the unit 1. The controller 7 is generally configured to receive from the one or more temperature sensors 7 a signal indicative of the temperature within the water storage unit 1. For example, in some embodiments the sensor 7 is a thermistor that creates a varying voltage that is dependent on the sensed temperature. The signal received by the controller 6 from the sensor 7 is a variable voltage indicative or representative of the temperature in the unit 1. Other temperature sensors that are equally as applicable comprise thermocouples and semiconductor band gap sensors. Figure 3 illustrates an arrangement for temperature sensing where a thermocouple 14 is located in thermo well 16 at or proximate to a hot water delivery pipe 18. The thermo well extends through an insulating wall 17 of the hot water storage tank such that the thermocouple is located close to the hot water leaving the storage tank to provide accurate measurement of that water. A source of power 3 is provided to the element 2 by way of the switch 4. The switch 4 is configured to apply and interrupt the source of power 3 from the element 2 in accordance with a control signal received from the controller 6. The source of power can also be optionally configured to provide power to the controller 6 via a connection 9, while in other embodiments, a separate source of power is provided to the controller.

Optionally, the system can be retrofitted to an existing hot water storage assembly comprising a hot water storage unit and a pre-existing temperature control device such as a thermostat. In these embodiments the switch is configured to operate in conjunction with or instead of pre-existing temperature control device. For example, where the unit is a domestic hot water cylinder with an existing thermostat, the switch is configured to be wired in series with the existing thermostat such that the source of power can be disconnected from the thermostat and thereby control operation of the heating element regardless of the thermostat being connected. Alternatively, a whole system comprising the control system of Figure 1, a hot water storage unit and associated plumbing is provided.

The system 10 may further comprise an interface 12 that is configured to receive control decisions or parameters from an external source, such as a user, and provide those decisions to the controller 6 via a connection 13. The interface can be for example a graphical user interface such as a touch panel configured to allow a user can enter information which the controller 6 may then use in control decisions. The controller 6 can be configured to output information to the interface 12 for display to a user. The connection 13 may comprise a serial communications bus such as RS485.

The controller is configured to control the temperature of the water within the storage unit 1 to a temperature below that which it would normally be stored. For example, if the normal storage temperature of the water is 60°C, the controller is configured to lower the water temperature to less than 60°C by selective disconnection of the power source from the heating element. A specific storage temperature can be targeted based on feedback from the one or more temperature sensors. The interface 12 allows input of a desired target temperature. The specific target temperature can be, for example, in the range of at least one of 30°C to 60°C, 35°C to 60°C, 40°C to 60°C, 45°C to 60°C, 50°C to 60°C or

55°C to 60°C, 30°C to 55°C, 30°C to 50°C, 30°C to 45°C, 30°C to 40°C, 30°C to 35°C, 30°C to 35°C, 35°C to 40°C, 40°C to 45°C, 45°C to 50°C, 50°C to 55°C, 55°C to 60°C, 40°C to 60°C or 40°C to 45°C.

Figure 2 shows an example embodiment of the system 15 where a domestic hot water cylinder 20 has a temperature sensor 21 adapted to provide a signal 22 indicative of the temperature of water in the cylinder to a controller 23. In some embodiments, the controller 23 and a switch 24 are integrally housed as shown. The switch is configured to connect and disconnect an incoming source of power 26 to provide a source of switched power 25 to a heating element adapted to heat water in the cylinder 20. An interface 27 is connected to the controller 23 by a serial communication link 28. The interface is configured to allow a user to select a desired target storage temperature from 40°C to 60°C in 5°C increments.

The controller 6 is configured to receive from the one or more temperature sensors one or more signals indicative of one or more values corresponding to the temperature of the water in the hot water storage unit. When the one or more signals are received, the controller is configured to statistically select one of the signals or combine the signals to determine a useful measure. For example, the measure could be an average or median, maximum or minimum value. The measure is then representative of the temperature of the water in the water storage unit.

The controller 6 is further configured to store a value indicative of a desired temperature of the water in the hot water storage unit. The desired temperature can be

predetermined. Alternatively, the desired temperature can be input, for example, by a user via the interface 12.

The controller is configured to compare the stored value (representing the desired temperature) and the received value (representing the actual temperature). The controller is further configured to output a signal to activate the switch 4 such that power is applied to the heating element when either:

• the received value is below the stored value, or

• the received value is below a combination of the stored value and a further value stored by the controller that is indicative of a tolerance temperature range.

The controller can be configured to provide power to the heating element 2 when the temperature of water in the storage unit 1 is below a desired temperature and disconnect power from the heating element when above a desired temperature. This provides tightly regulated control of the stored water temperature.

Alternatively, the controller is configured to energise the element 2 when the

temperature of water in the storage unit 1 is below a combination of the desired temperature and a variable tolerance range. The combination is in effect an extension on the threshold before which the heating element 2 is energised to heat the water. This provides a form of hysteresis by allowing the water temperature to fall further from the desired temperature, yet avoids frequent connection and disconnection of the heating element as the water temperature rises and falls above the desired temperature. The hysteresis range is easily tuned by alteration of the value representing the tolerance temperature range. A value representing the tolerance range can be stored in the controller. Alternatively, the value representing the tolerance range is provided by a user and input via a control panel.

The controller can be configured to alter the value representing the tolerance

temperature range based on whether the storage unit 1 experiences, or is predicted to experience, high or low water usage. The controller can be configured to make a determination of high water usage when temperature of water in the storage unit 1 drops below the desired temperature by a threshold value. The threshold value can be a value indicative of the temperature of the water in the storage unit 1 dropping by 10°C below a desired temperature. The controller is configured to periodically make at least one measurement of the water temperature. That period can be the course of one hour, for example. The controller is configured to statistically treat or combine multiple

measurements to determine a useful representative measure of the water temperature over the previous hour. For example, the measure could be an average or median, maximum or minimum value.

In the embodiment described, the controller is configured to store information for each of a plurality of time period parameters. As an example, the time period parameters can each represent a period of one hour for each hour of day of a seven day cycle. The information stored is a determination of whether high or low water usage occurs for each of those hours. Other embodiments have different time periods and particular time periods used may be linked to factors including the volume of the hot water storage unit and/or the location of the unit, for example, whether it is located in a low hot water use or high hot water use environment. The outcome of this process is a set of data representing high or low water usage for each hour of the previous week. The

determination of high or low water usage for each hour is used to set the tolerance range which affects the energisation hysteresis range of the heating element 2. In some embodiments the tolerance range is 5°C below the desired temperature for a time period parameter with the determination of high water usage, and 6°C below the desired temperature for a time period parameter with the determination of low water usage. Generally, when particular hours of the day are determined to be those where low amounts hot water is used, the controller is configured to allow the temperature of the hot water in the storage unit to drop further below the desired temperature. This is because energy can be saved by not immediately heating the water and because there is a low risk of hot water running out. During particular hours of the day determined to be those where high amounts hot water is used, the controller is configured to try to keep the temperature of water in the storage unit closer to the desired temperature such that the risk of running out of hot water is reduced. Figure 4 illustrates a flow diagram of the steps undertaken by the controller used for determining whether high or low water usage occurs for each one of a plurality of the time period parameters. At step 50, the controller determines a measure of the temperature of water in the storage unit and compares that measure to a temperature threshold. If the measured temperature is more than 10°C, or some other threshold, below a desired temperature the current hour is determined to be a high usage hour. At step 51, the controller sets a high usage hour parameter and stores that parameter for that hour in a weekly cycle at step 52. If the measured temperature is less than 10°C, or some other threshold, below a desired temperature the current hour is determined to be a low usage hour. At step 53, the controller further determines whether the particular current hour for the same hour in the prior seven days has all been determined to be a low usage hour. At step 54 the controller sets the hysteresis or tolerance temperature range 6°C if this is true. At step 55 the controller sets the hysteresis or tolerance temperature range 5°C if this is false. The process restarts and loops as often as is required. In some embodiments the process is repeated approximately every second.

The usage statistics can be recorded for each hour of a seven day cycle. Figure 5 illustrates a flow diagram of the steps undertaken by the controller used for processing water usage statistics on a daily basis. For every 24 hours that pass, a day parameter is shifted forward by one day. The usage statistics for the previous day are recorded against the previous day in a table. The current day statistics are cleared and new data is recorded. For example, if the water temperature falls 10°C below the desired

temperature in any given hour, that hour in the seven day cycle will be recorded as a high usage hour for that day. If all of the current hour statistics for each of the seven previous days are recorded as low usage hours, the hysteresis or tolerance range is set to 6°C. Alternatively, if all or some of the current hour statistics for the seven previous days are recorded as high usage hours, the hysteresis or tolerance range is set to 5°C. According to some embodiments, each hour is set to be a high usage hour the first time the controller is powered.

Figure 6 illustrates a flow diagram of steps undertaken by the controller to control general heating operation of the hot water storage tank in accordance with some embodiments. The controller is configured to repeat the control steps as quickly as required and can be as often as every second. The controller receives the one or more signals from the one or more temperature sensors at step 30 and stores a measure of the temperature in the storage unit. A determination is made of whether the received temperature sensor measurements are sensible at step 31. If the measurements are not sensible, the controller is configured to maintain the temperature measured prior. Signal errors may occur due to wired disconnections, power outages, glitches and other such inadvertent causes. The controller is configured to monitor for several contiguous measurement errors at step 33 and switches the heating element off at step 35 if this is true. Measurement errors are often indicative of a more serious problem and switching off of the element provides a level of safety by, for example, ensuring overheating of the water does not occur.

At step 36, the controller is configured to compare the measured water temperature to 60°C. The element is switched off the water is more than or equal 60°C. At step 37, the measured water temperature is sent for display on the user interface.

Steps 38, 39 and 40 relate to checking the signals received from and transmitted to the user interface are free of errors. The element is switched off at step 47 if five signal errors are detected.

At step 41, the controller is configured to compare the measured water temperature to a desired water temperature that has been predetermined, stored or input via the user interface. If the controller determines the measured temperature is less than or equal to the desired temperature, the controller is configured to compare the measured temperature to the hysteresis temperature threshold at step 43. The controller is configured to activate the switch at step 44 such that the heating element is energised if it is determined that the measured temperature is less than or equal to the hysteresis temperature threshold. Following step 44, the controller is configured to restart the process. Alternatively, the controller is configured to restart the process if it is determined that the measured temperature is greater than the hysteresis temperature threshold

A bacteria killing cycle or 'biocycle' is where the water in a water storage unit (that is otherwise controlled to a temperature that is lower than 60°C) is heated to at least 60°C after a period of time. The controller can be configured to initiate a biocycle process when desired. The biocycle process comprises periodically heating water to a

temperature adequate for killing bacteria such as legionella.

At step 42 the controller is configured to check whether a biocycle has or is to be initiated if it is determined that the measured temperature is greater than the desired temperature. If not, the controller is configured at step 47 to switch off the heating element. If so, the controller is configured at step 45 to determine whether the measured water temperature is greater than or equal to 60°C. If so, the controller is configured at step 46 to deactivate any biocycle. If not, the controller is configured to the controller is configured to restart the process. Therefore, the system allows for the lowering of the water temperature in a hot water storage unit while also tracking water usage so as to mitigate the risk of running out of hot water entirely.

Improved bacteria control In other particular embodiments the controller is configured to periodically initiate a bacteria killing cycle in an adaptive manner which is improved from the one described above. In the improved bacteria killing cycle the controller is configured to periodically determine the temperature of the water and calculate an accumulative statistical measure of the temperature. The accumulative average temperature can be calculated and compared to a threshold that represents a period of time and upon the elapse or surpassing of that period of time the bacteria killing cycle is initiated. When a bacteria killing cycle has been completed, the controller resets the accumulative statistical measure of that temperature and period of time values and the process repeats.

Generally, the bacteria killing cycle is initiated frequently when the temperature of water in a water storage unit is kept well below 60°C, whereas the bacteria killing cycle is initiated less frequently when the water temperature is kept near 60°C. The relationship between the time delay before a bacteria killing cycle is initiated and the average temperature generally increases as the average temperature increases. The average temperature is calculated based on a running average of temperatures over a period of time since the last bacteria killing cycle was performed. In preferred embodiments the relationship between the average water temperature and the time delay before a bacteria killing cycle is initiated nonlinearly increases, or is somewhat exponential in form. This improved bacteria killing cycle may be implemented as part of the control process with any one of the above described embodiments or it may be implemented as part of a pre- existing system.

The bacteria killing cycle can be initiated when the threshold that represents the period that has elapsed and it has been determined by the above described process that the present hour has been determined to be one of low water usage. Further, the controller can be configured to initiate the bacteria killing cycle upon the lapse of twenty three hours if there are no hours determined to be low water usage hours within the next twenty four hours or by the end of the current day.

Figure 8 illustrates flow diagrams outlining detailed processes undertaken by the controller in accordance with to particular embodiments. Generally, the controller is configured to periodically heat the water to a temperature that kills bacteria, such as 60°C, then return to normal operation. The timing of the bacteria killing cycle is based on the average water temperature. The water temperature is determined at regular intervals, summed and divided by the number of readings made. The average

temperature over the past twenty four hours is determined. At the end of each twenty four hours, the controller is configured to check to see if the bacteria killing cycle is required within the current day, and if so, a day counter is reset to a maximum of twenty two days. When the bacteria killing cycle is desired the controller is configured to initiate the cycle on the first occurrences of a low usage hour based on the statistics for that day. The bacteria killing cycle is initiated at the beginning of the twenty third hour of that day if the controller determines there are no low usage hours within the next twenty three hours. The controller can store a look up table that specifies the number of days that may elapse for a particular average temperature before the bacteria killing cycle is initiated. Alternatively or additionally, the controller calculates the days that may elapse for a particular average temperature based on a mathematical formula or model.

Figure 8(a) shows that approximately every six minutes the controller is operable to, at step 60, measure the current water temperate and sum the temperature with any previously measured temperatures. At step 61, the controller is configured to increments a counter representing how many measurements have been made. The controller is further operable to compute the average water temperature by dividing the sum of the temperatures by the number of temperature readings recorded. Figure 8(c) shows that approximately every 24 hours the controller is operable at step 62 to compute a day counter variable or countdown timer indicative of when the next initiation of a bacteria killing cycle is due to be initiated. At step 63 the controller determines whether the day counter variable has reached a target based on the accumulated average temperature. At step 64 the controller makes a determination or sets a flag indicating that the bacteria killing cycle is due if the target is reached. At step 65 the controller then resets the day counter to a maximum day value and restarts the program. The maximum time between bacteria killing cycles can be twenty two days, for example. At step 66 and 67 the controller calculates a new accumulated average temperature if the target is not reached. At step 68 a new target day counter variable is determined based on the newly determined accumulated average temperature. The target day counter variable could increase depending on whether the accumulated average temperature has risen or fallen. At step 69 and 70 the controller determines whether the new target day counter variable is less than or equal to the previous value which would indicate a bacteria killing cycle should be initiated. Figure 8(b) shows that approximately every hour the controller is operable to determine whether a bacteria killing cycle is due to be initiated. At step 71 the controller determines whether a determination, such as a flag, has been set and at step 72 determines whether the present hour is an hour determined to be a low water usage hour for each of the last seven days. At step 74 the controller determines the bacteria killing cycle should occur and causes energisation of the heating elements at step 75 if the present hour is a low water usage hour.

The controller may implement any one or more of the following additional control steps:

• The controller is configured to switch off the heating element and not reenergise the heating elements until the water temperature drops to the minimum hysteresis temperature if any temperature over 60°C is determined. · The controller stops operating the heating element until a user manually restarts the controller operation by the interface 12 if the controller is unable to read a

temperature sensor.

• The controller periodically polls the interface 12 to determine an operable connection.

If the controller determines there is no operable connection, the controller stops operating the heating element until the interface is reconnected.

• The controller is configured to periodically check the integrity of the data relating to water usage. If the controller determines the data is lacking integrity, a default set of data is reverted to and a bacteria killing cycle is initiated.

• The controller is configured to resume its last known operation should there be a power outage.

• The controller is configured with a 'watchdog timer' that restarts operation should an internal process take an inordinate amount of time.

Figure 7 shows a graph of ideal time periods that elapse for an accumulative average temperature of the water in the water storage tank before the bacteria killing cycle is initiated. In particular:

• the time threshold is approximately three days if the accumulative average

temperature is less than 40°C,

• the time threshold is approximately five days when the accumulative average

temperature is approximately 40°C to 45°C,

· the time threshold is approximately nine days when the accumulative average

temperature is approximately 45°C to 50°C,

• the time threshold is approximately thirteen days when the accumulative average temperature is approximately 50°C to 55°C, and/or • the time threshold is approximately twenty one days when the accumulative average temperature is approximately 55°C to 60°C.

Table 1 ideal day cycles for accumulative average temperature

Therefore the system is able to mitigate the risk of allowing harmful bacteria to grow whilst still enabling potential energy savings to be achieved by allowing a lowering of the water temperature in the hot water storage unit. Experimental results

Hot water controller embodiments of the invention were compared to hot water control systems of the prior art which was a bimetallic strip thermostat type hot water controller. The heating element for the hot water storage unit comprised a 2000 Watt heating element. The electrical energy consumed by the heating elements controlled by each controller was measured using a Seimens S2AS electricity meter with a 0.001 kWh resolution. The water flow from each hot water storage unit was measured using a ManuFlo MES-25 water flow meter with a 0.03 L resolution. A plurality of T-type thermocouples were located around the hot water storage unit to measure the temperature of the water. A valve was connected to the outlet of each hot water storage unit to periodically release water. The water was released to simulate the typical 'draw- off. At one minute intervals, information output form of the electricity meter, water meter and thermocouples was recorded. Information was recorded for a period of thirty four days.

Table 2 provides an example of typical draw-off data that may be exhibited by a normal a household and data that is frequently used in solar water heating standards work and includes data relating to energy use during particular periods of the day.

Hour of day Standard schedule 7.00 0.150

8.00 0.150

11.00 0.100

13.00 0.125

15.00 0.125

16.00 0.125

17.00 0.125

18.00 0.125

Table 2 Draw-off schedule (proportion of energy)

Figure 9 shows an example of logged temperature of the water stored in a water storage unit controlled in accordance with some embodiments of the invention 80 and controlled using a bimetallic strip type thermostat 81 of the prior art. The thermostat of the prior art 81 is configured to power and depower the heating element to maintain the water temperature at temperatures around 60°C without deviating significantly from that temperature. In contrast, the invention is configured, in this example, to maintain a water temperature of approximately 45°C. Figure 9 shows that the water temperature is raised 83 to approximately 64°C to perform a bacteria killing cycle after a period of approximately five days elapses. The total energy consumption when maintaining a lower set temperature and periodically initiating a bacteria killing cycle is less overall than maintaining the water temperature at a substantially fixed higher temperature. Figure 10 shows a bar graph of system energy use performance of the controller of the prior art based on the water usage and temperature, while Figure 11 shows a bar graph of the same data controlled in accordance with some embodiments of the invention. The controller of Figure 11 exhibits 16% less total energy consumption than the controller of Figure 10, or a total energy saving of approximately 162 kWh over a four week period. Table 3 provides information of the measured energy, draw off energy and system energy for each week of a four week period. The system energy for the control system of Figure 10 averaged approximately 1.9 kWh per day. The system energy for the control system of Figure 11 averaged approximately 0.8 kWh per day and therefore exhibits a 1.1 kWh per day improvement in daily efficiency.

Standard Cylinder TESS controlled Cylinder Mean Daily Daily

Daily eas. Daily Draw off Daily Meas. Daily Draw

Ambient System System

Energy Energy Energy off Energy

Temp Energy Energy

(kWh/day) (kWh/day) (kWh/day) (kWh/day)

(°C) (kWh/day (kWh/day)

Cycle 1

26 Dec- 22.7 7.0 5.0 2.0 5.9 5.0 0.9

1 Jan

Cycle 2

2 Jan-8 23.1 7.1 5.0 2.1 5.8 5.0 0.8 jan

Cycle 3

9 Jan-15 23.7 6.7 5.0 1.7 5.8 5.0 0.8

Jan

Cycle 4

16 Jan- 24.3 6.8 5.0 1.7 5.7 5.0 0.8

22 Jan

Overall

26 Dec- 23.5 6.9 5.0 1.9 5.8 5.0 0.8

22 Jan

Table 3 Average energy use over each of the Legionella cycles

Where in the foregoing description reference has been made to elements or integers having known equivalents, then such equivalents are included as if they were individually set forth. Although the invention has been described by way of example and with reference to particular embodiments, it is to be understood that modifications and/or improvements may be made without departing from the scope or spirit of the invention.