A Controllable Water Heater

Field of the invention

[001 ] This invention relates to a controllable water heater.

[002] The invention can be used to control the operation of a water heater so that it can operate during times when electricity tariffs are low.

Background of the invention

[003] Water heater installations are known which are controlled by ripple control signals transmitted by the electricity supply utility over the power lines so that the water heater operates during off-peak periods. In these arrangements, the electricity utility supplier injects a ripple frequency signal into the mains power lines and this is detected at the houses of consumers fitted with off-peak meters so the water heaters can be switched on during low demand periods and switched off during high demand periods. The ripple signal is detected at the consumer's switchboard and a relay at the switchboard turns off the power to mains power line to which the water heater is connected. This means that there is no power supplied to the water heater which is often located remote from the switchboard. Thus, there is no power available to the heater during the periods when the ripple controller cuts the power to the heater.

[004] The water heater used for this sort of off-peak system is usually of the same kind suitable to be used with continuous power supply.

[005] The off-peak control circuit was metered through a separate meter from the standard rate meter so that the consumption of off-peak electricity could be identified separately from the standard rate consumption.

[006] Electricity supply utilities are now proposing to introduce or have introduced variable tariffs which may have three or more different tariff rates. These tariffs can be applied on a time-of-day basis, or they may be responsive to the load on the generation system. The tariff rates can be applied to all the appliances at a consumer's premises. To achieve this, either all the load would need be switched between two meters, or a so called smart meter can be used which is capable of recording the consumption together with the time of day of the consumption, and/or the applicable tariff rate for the consumption.

[007] A smart meter is a meter which is "aware" of the time of day or which has a degree of programmability such as a processor controlled meter. The meter may have the capability to record consumption together with the time of day. Such a meter may also include

some communication capability, such as an interface to a modem, to enable the utility supplier to communicate with the meter, for example, to read the meter. The meter may also be responsive to signals from the utility indicative of the prevailing tariff rate. The meter may also include a time of day clock.

[008] The electricity supply utilities are proposing to install smart meters which are able to accommodate the changes in tariff rate, so that a single meter can differentiate between consumption at the different tariff rates. The smart meters are programmable to determine the appropriate tariff. This may be done by the use of a time-of-day-clock or by sending a message to the meter via a communication link such as the power lines, a wireless link, or a telephone line etc from a control point. The smart meters can also include a keypad and display to enable tariff rate schedules or programs to be entered manually.

[009] Typically, in a domestic electricity supply using electrical water heating, the electricity used for the water heater is more than 20% of the total consumption.

[010] Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application.

Summary of the invention

[011] In a first embodiment, the invention provides an electrical water heater having a switch to operate heating means which is located in the water heater, and a switch controller controllable to make power available to the element during selected periods.

[012] The heating means can be a suitable heat source such as, for example, a resistive heating element or a heat pump.

[013] The invention also provides an electrical water heater switch arrangement adapted to be connected to an electrical water heater, the switch arrangement including a switch connected to control an electrical heating means, and a controller adapted to make power available to the heating means during selected periods.

[014] Such a switch arrangement can be retrofitted to existing electrical water heaters.

[015] The controller can be responsive to a tariff related input signal to turn the element off during high tariff periods.

[016] The controller can include a timer control which is set to interrupt power to the element during first periods, which would normally be high tariff periods, and to make power

available to be supplied to the element during second tariff periods, which would normally be low tariff or off-peak periods. The controller can be programmed to achieve the same effect by pre-selecting the uninterrupted periods.

[017] The controller can be programmed to implement a randomized delay at the beginning and/or end of the interruption. This will assist the power supply utility in that a switching surge could otherwise occur if a large number of such controllers were to switch at the same time.

[018] The timer can be synchronized to a time-of-day signal to within a tolerance time window.

[019] The controller can be responsive to an output from a smart electricity meter to select non-peak tariff periods in which to operate the heater.

[020] The controller can be responsive to a time signal provided over a communication link.

[021 ] The controller can be responsive to a time signal provided from a smart electricity meter.

[022] The controller can be responsive to a tariff signal provided by a smart electricity meter.

[023] The controller can be responsive to a tariff signal provided over a communication link.

[024] The controller can be responsive to a time signal provided over the power distribution line by a utility or agent.

[025] The controller can be responsive to a tariff signal provided over the power distribution line by a utility or agent.

[026] A back-up power supply can be provided to maintain the controller operational during a power outage.

Brief description of the drawings

[027] An embodiment or embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[028] Figure 1 is representative illustration of the daily load for an electricity utility;

[029] Figure 2 a schematic representation of a water heater embodying the invention; and

[030] Figure 3 is a block diagram illustrating a controller according to an embodiment of the invention.

[031 ] Figure 4 illustrates a further embodiment of the invention.

Detailed description of the embodiment or embodiments

[032] An advantage of having the cut-off switch co-located with the heater is that power is still available at the heater to supply an electronic controller which is part of the heater control system.

[033] Figure 1 shows an illustrative graph of the load against time-of-day of an electricity utility. The load has been split into a number of levels to which the utility provider allocates different tariff rates, such as Tl, T2, and T3.

[034] Tl is the tariff applied during the lowest load period, and, for example, would commence about 22:00 at a time indicated by line 110, and last until about 06:00 the next morning as indicated by line 104.

[035] The load may then shift to an intermediate level, on the right of line 104, at which a second tariff T2, higher than Tl is applied.

[036] A peak load tariff is applied as the load crosses the T3 line at a time indicated by line 106. This load may stay above the T3 level until a time indicated by line 108, or as in the case illustrated in the Figure 1 by lines 112, 114, it may dip below the peak load line T3 for one or more periods before the time indicated by line 108.

[037] At the end of the peak period, line 108, the load falls through the intermediate load level to line 116 and may continue to fall below the intermediate load level T2 into the ^• lowest load zone where tariff Tl applies.

[038] The load may then rise above the Tl zone back to the T2 zone between lines 118 and 110.

[039] Thus there can be several changes of load level during a daily load cycle.

However, the pattern of such load variations may vary from day to day, and the utility supplier may choose not to vary the tariff at each load change, but only at major changes where the load changes for a minimum period. Thus, for example, the utility provider may choose not to change tariff rates between lines 112 and 114 and between lines 116 and 118. hi this way the tariff

provider can limit the number of tariff changes during a day. Thus the number of tariff changes may be limited to three or four changes per day. Provided the load pattern is reasonably predictable, the tariff changes can be expected to fall within predictable time periods during a day under normal circumstances.

[040] Thus a water heater with a suitable timer can be set to operate outside the peak tariff period T3.

[041] The water heater can be set to operate during the minimum tariff period.

[042] The water heater can be set to operate preferentially during the lowest tariff period, while being programmed to operate during a higher tariff period where the temperature of the water falls below a minimum threshold value.

[043] The water heater can be set to operate preferentially during the lowest tariff period, while being programmed to operate during a higher tariff period where the temperature of the water falls below a minimum threshold value, and there is an actual demand for hot water.

[044] The water heater can be set to operate preferentially during the lowest tariff period, while being programmed to operate during a higher tariff period where the temperature of the water falls below a minimum threshold value, and there is an expected demand for hot water.

[045] Figure 2 illustrates an embodiment of a water heater having a controller 224 adapted to control the operation of an electrical heating element 222 in a storage water heater tank 220. The controller can be a stand alone device or can be connected to a smart meter, and/or to one or more communication links. Figure 2 shows an optional link 212 between a smart meter 202 and the controller 224. The smart meter can be programmed to register the different tariff periods, and it can be provided with an output to indicate the current tariff rate to the controller 224 via link 212. Alternatively, the smart meter can be adapted to communicate this information using a local wireless link and a suitable communication protocol such as Bluetooth or 802.11 as shown illustratively by antennas 208, 230.

[046] Instead of receiving the tariff information from the smart meter, the controller 224 may be programmed to track the time-of-day on a stand-alone basis, and to control the operation of the heater accordingly.

[047] In a further embodiment, the controller can be synchronized with an external clock 236 to which the controller 224 is connected by a communication link such as a phone line 232, or an internet connection over the phone line 232.

[048] The controller may alternatively use a wireless connection to communicate with the utility or an external clock via a wireless communication network. The antenna 230 may be taken as being illustrative of either the local wireless capability or of the wireless communication network capability of the controller 224 depending on which mode of communication is used. In a further embodiment, the controller can include both the local wireless communication capability and the external wireless communication capability.

[049] Details of an embodiment of a controller using microprocessor control are shown in Figure 3.

[050] The heater 322 is operated by relay contacts 340 of relay 348. The controller includes a microprocessor 342, a memory 344, a number of peripheral ports 350, one or more communication interfaces 356, and relay control 346. These elements are shown as communicating over bus 358, but may be operatively connected in different configurations.

[051 ] In addition, the controller can receive information from sensors, represented by block 360, associated with the tank 220, such as temperature sensors disposed at various depths within the tank 220. The use of a number of temperature sensors at different depths is advantageous where top down heating is applied in the tank 220 or where different operating modes are to be made available.

[052] The controller 300 also includes a power supply 362. The power supply is connected "upstream" of the switch 340, so that, when the switch is open, power is still available for the controller.

[053] Switch 340 is also responsive to the temperature sensors 360, so that the switch is closed during the off-peak periods and when the temperature is below the operating temperature range, while switch 340 will be open during the off-peak period if the temperature is within the operating range.

[054] In a first embodiment, the controller maintains a time-of day clock and is programmed to switch the heater element on only during the lowest tariff periods. Where the tariff periods vary with the actual load experienced by the utility, the controller can be adapted to ignore the variations on the assumption that the higher tariff will only be applicable for a short time while the heater element is activated. Alternatively, the controller can be programmed with a guard delay time designed to ensure that most of the time the heater will only be turned on when the tariff has dropped to the lowest value.

[055] As a refinement of this embodiment, the controller 224 can be periodically synchronized with an external time-of-day signal provided via a wireless link through antenna 230 or via a phone or internet link through line 232.

[056] In a further embodiment, the controller can be responsive to an input signal alerting it to the current tariff status. This signal can be derived from the smart utility meter, or from the utility provider via a communication link.

[057] In the case where the controller is informed of the current tariff by the smart meter, the information can be conveyed via line 212, or via a wireless link using the antennas 208 and 230.

[058] An advantage of having the off-peak switch located at the water heater is that power is still available for the controller 300. Thus the controller processor can be powered and maintain its processing and memory functions. A back up power storage means, such as a battery or large capacity capacitor can be provided to maintain power to the controller during power interruptions. Of course, programming and memory can be stored in non- volatile memory.

[059] In the embodiment shown in Figure 4, a transformer 445 has been included shunting the series switch 440. The transformer is connected into the power circuit by switches 441, 443 which operate in antiphase to switch 440, so that when switch 440 is closed, switches 441 and 443 are open. When switch 440 is closed, switches 441 and 443 can be closed if the temperature is below the operating threshold. Thus, when the transformer 445 is a step down transformer, the water heater can still draw power from the grid, but it will draw less power than when power is supplied to the heating element 422 via switch 440.

[060] The incorporation of power control means, such as provided by the transformer

445, means that there are three possible modes of operation of the heating element, full power during off-peak periods, reduced power during medium load periods, and off during peak load periods.

[061] An alternative mode of operation is to program the controller so that it has two or more operating temperature ranges which are selected according to the load conditions or time of day. Thus the "normal" temperature operating range can be used during a first period corresponding with an actual or expected low system load, while a second temperature operating range, corresponding to an actual or expected intermediate system load, can be implemented by the hot water system controller. This second operating range can have an upper temperature limit lower then the upper temperature limit of the first operating range. A third mode would turn the

heater off when the peak load is reached. Use of the intermediate operating range would mean that, while the heater would still draw the same operating current, it would have a shorter overall duty cycle during the implementation of the second operating range. Where there are a plurality of hot water systems operating in this mode, the load will be randomly distributed.

[062] Switch 441 or 443 can be operated as a temperature control switch during the periods when switch 440 is open.

[063] Such a feature can be made optional to a user by enabling them to select the feature using the input keypad of the controller. The user input may be by way of a scrolling menu selection.

[064] The switch controller can incorporate sufficient processing power and memory to enable the controller to control the tariff switching functionality in a semi-autonomous manner, so that the controller can store the tariff change times for a time based system, or can be responsive directly to a tariff or time signal to control the tariff switching.

[065] A power line signal from the utility company or other reliable source can be used to periodically synchronize a clock incorporated in the controller.

[066] The hot water system controller can be arranged to communicate with the smart meter such that operating parameters of the hot water system can be displayed on the display of the smart meter. The smart meter can be provided with a menu via which the user can access the operational details of various appliances including the hot water system. The user can also control the operation of the hot water system via the smart meter input keypad. The hot water system controller can maintain records of the performance of the heater in its own memory or communicate these to the smart meter for storage. The hot water system can be an electrically boosted solar water heater or a heat pump water heating system.

[067] The controller can incorporate one or more of the following features: a stand-alone clock to control time-of-day switching; a synchronizable clock receiving a synchronization input from a communication link; a synchronizable clock receiving a synchronization input from a smart meter; a load based switching output generator responsive to a load or tariff signal from a communication link; a load based switching output generator responsive to a load or tariff signal from a smart meter the switch is integrated into hot water system;

there is provision for powering for hot water system controller during off-peak; the system can provide randomized or off-set switching to reduce the switching spikes; a bypass transformer can be provided to reduce power consumption during peak load periods; the tariff/load control feature can be incorporated in the hot water system controller.

[068] The off-set can be arranged so that, in each switching block, at least some of the meters will switch at different times within a time window.

[069] The invention also provides an electrical water heater switch arrangement adapted to be connected to a water heater, the switch arrangement including a switch connected to turn control an electrical heating element, and a controller adapted to make power available to the element during lower tariff periods. The switch arrangement can be incorporated in a "bolt- on" pod which can be attached to the housing of a water heater. The pod can be incorporated into an element cover of a water heater. Such a switch arrangement can be retrofitted to existing electrical water heaters.

[070] The controller can also be provided in a self-contained box or cover in which the controller is in series between the heater and the power meter.

[071] In the description, unless the context requires otherwise, the term "signal" is understood to include an analog signal or digital signal including one or more bits. Such signals can be interpreted according to a communication protocol to have a defined meaning or to convey information.

[072] Where ever it is used, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

[073] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention.

[074] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all

modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.