Thermal storage device

Abstract

According to a first aspect of the disclosure, a thermal storage device is provided. The thermal storage device comprises a thermal storage core, a plurality of heating elements, a temperature sensor, and a safety temperature threshold circuit. The thermal storage device also comprises a circuit breaker circuit for each of the plurality of heating elements. The thermal storage core is configured to store thermal energy. The plurality of heating elements are each configured to heat the thermal storage core. The temperature sensor is disposed in the thermal storage core and configured to output a temperature signal representative of a temperature of the thermal storage core. The safety temperature threshold circuit is configured to receive the temperature signal and output a safety signal when the temperature signal indicates that a temperature of the thermal storage core is below a safety temperature threshold of the safety temperature threshold circuit. Each circuit breaker circuit is configured to allow the supply of electrical energy to the respective heating element upon receiving the safety signal from the safety temperature threshold circuit. When the safety signal is not received, each circuit breaker circuit is configured to prevent the supply of electrical energy to the respective heating element.

Description

[0001] Thermal storage device

[0002] Field of the disclosure

[0003] The present disclosure relates to heating devices. In particular, the present disclosure relates to a thermal storage device.

[0004] Background

[0005] Thermal storage devices, also referred to as dry core thermal storage devices, thermal storage boilers, dry core storage boilers, heat banks, heat batteries, storage boilers or zero emission boilers, convert electrical energy into heat using electrical heating elements or resistive heating elements and store the heat in a core material, or storage medium, located in a core. The heat is usually transferred from the core material by a fan driving a transfer fluid, such as air, between the core and a heat exchanger in a closed loop. The heat exchanger transfers the heat to a water and / or central heating system for delivering heated water as required. Typically, the thermal storage devices consume electrical power at times of low demand (or excess generation) across an electricity grid or network, such as during the night, when it has a lower cost. Increasingly, this can occur at any time of day due to the increase in generation from renewable sources. One such thermal storage device is disclosed in WO-A-2021037865.

[0006] The core material in the core operates up to a very high temperature. Normal operating temperatures may be up to 800°C. If not controlled, the electrical heating elements or resistive heating elements can heat the core material to even higher temperatures. At very high temperatures the core material may undergo undesirable changes. For example, it may be desirable to prevent the core material reaching temperatures of around 1200°C. To prevent such high temperatures, a thermal control system can use software to regulate the amount of electricity being supplied to the electrical heating elements or resistive heating elements. The temperature in the core material can be monitored using thermocouples or other devices suitable for measuring high temperatures. This measurement can be used to monitor the device and provide feedback for a software- based control system.

[0007] The present disclosure aims to provide an improved, or at least a commercially relevant alternative, thermal storage device. Summary

[0008] According to a first aspect of the disclosure, a thermal storage device is provided. The thermal storage device comprises a thermal storage core, a plurality of heating elements, a temperature sensor, and a safety temperature threshold circuit. The thermal storage device also comprises a circuit breaker circuit for each of the plurality of heating elements. The thermal storage core is configured to store thermal energy. The plurality of heating elements are each configured to heat the thermal storage core. The temperature sensor is disposed in the thermal storage core and configured to output a temperature signal representative of a temperature of the thermal storage core. The safety temperature threshold circuit is configured to receive the temperature signal and output a safety signal when the temperature signal indicates that a temperature of the thermal storage core is below a safety temperature threshold of the safety temperature threshold circuit. Each circuit breaker circuit is configured to allow the supply of electrical energy to the respective heating element upon receiving the safety signal from the threshold safety circuit. When the safety signal is not received, each circuit breaker circuit is configured to prevent the supply of electrical energy to the respective heating element.

[0009] Accordingly, the thermal storage device is provided with a safety temperature threshold circuit and a plurality of circuit breaker circuits which are configured to prevent the supply of electricity to the heating elements in the event that the temperature of the thermal storage core exceeds a safety temperature threshold. It will be appreciated that the circuit breakers circuits are each configured to allow the supply of electrical energy to the heating elements upon positively receiving a safety signal. As such, the circuit breaker circuits and the safety temperature circuit operate in a fail-safe manner in that the absence of the safety signal causes the circuit breaker circuits to prevent the supply of electricity to the heating elements.

[0010] According to the first aspect, the temperature sensor is provided within the thermal core. Thus, the temperature sensor is positioned within the thermal storage device to determine a temperature of the thermal storage core which is representative of the thermal energy stored within the thermal core. Accordingly, the temperature signal output by the temperature sensor is representative of the temperature of the thermal storage core. By contrast, locating a temperature sensor on the outside, or proximal to, the thermal storage core may not accurately, or promptly, record changes in the temperature of the thermal core. In order to reduce, or prevent, excessive heating of the thermal storage core, the thermal storage device of the first aspect provides a temperature sensor and associated circuitry which responds promptly to changes in the temperature of the thermal storage core.

[0011] The thermal storage device of the first aspect comprises a plurality of heating elements, preferably at least three heating elements. The heating elements may be evenly distributed (e.g. evenly spaced apart) within the thermal storage core in order to evenly heat the thermal storage core. A temperature sensor positioned within the thermal core is configured to output a temperature signal representative of a temperature of the thermal storage core. The temperature sensor may be configured such that the temperature may be representative of the temperature of the thermal storage core surrounding each of the heating elements. As such, a single temperature sensor may be provided within the thermal storage core for monitoring the temperature of the thermal storage core surrounding each of the plurality of heating elements. According to the first aspect, the safety temperature threshold circuit is configured to allow / prevent the supply of power to each of the heating elements based on the temperature signal from the single temperature sensor. As such, a thermal control system for a thermal storage device may be implemented in an efficient manner.

[0012] It will be appreciated that the safety temperature threshold circuit and the plurality of circuit breaker circuits may each be implemented entirely in hardware, rather than software-based control. That is to say, the safety temperature threshold circuit and the plurality of circuit breaker circuits may each be formed from discrete electronic components in order to provide a robust, fail-safe thermal control system.

[0013] In some embodiments, the thermal storage device comprises a controller configured to control the thermal storage device, wherein the controller is configured to control each of the plurality of circuit breaker circuits in order to control the supply of electrical energy to each of the plurality of heating elements in addition to the safety temperature threshold circuit. As such, in some embodiments, the thermal storage device may be provided with a controller (e.g. a microcontroller or processor) which provides software-based control over each of the heating elements in addition to the hardware-based safety control provided by the safety temperature threshold circuit and the plurality of circuit breaker circuits. It will be appreciated that the safety temperature threshold circuit controls the plurality of the circuit breaker circuits independently of the controller such that the absence of the safety signal from the safety temperature threshold circuit causes the circuit breaker circuits to prevent the supply of power to the heating elements, overriding any signals from the controller.

[0014] In some embodiments, the controller is configured to determine an operational state or a non-operational state of each of the plurality of the heating elements. As such, the controller may provide a software- based determination of the operating state for each of the heating elements. For example, the controller may have access to other sensor information from the thermal storage device (e.g. a temperature associated with the controller or other part of the heating device) in order to determine whether the plurality of heating elements should be in an operational state or a non-operational state. Upon determining the non-operational state for one or more of the heating elements, the controller is configured to control the circuit breaker circuits associated with the one or more heating elements having the non-operational state to cause said circuit breaker circuits to prevent the supply of electrical energy to the associated one or more heating elements. For example the controller may determine there is fault associated with the supply of electrical energy to one of the heating elements (e.g. a faulty heating element), while other heating elements remain operational. In such a case, the controller may control the circuit breaker circuits to supply electrical energy to the heating elements in the operational state, and not to the heating elements in the non-operational state.

[0015] In some embodiments, the controller is configured to determine a temperature associated with each of the heating elements and to obtain an operational temperature threshold associated with each of the heating elements, wherein the controller is configured to determine an operational state or a non-operational state of each of the plurality of heating elements based on the temperature associated with the respective heating element and the operational temperature threshold for the associated heating element. As such, in some embodiments, the controller may also monitor the temperature of the heating elements independently from the safety temperature control threshold circuit, wherein the controller can prevent the supply of electrical energy to the heating elements in the event that the operational temperature threshold is exceeded. Thus, the thermal storage device may be provided with two independent temperature monitoring functions which can act to prevent the supply of power to the heating elements in the event that a temperature threshold is exceeded. In some embodiments, the operational temperature threshold associated with each of the plurality of the heating elements is lower than the safety temperature threshold of the safety temperature threshold circuit. As such, the operational temperature threshold used by the controller may be set to be exceeded at a lower temperature of the thermal storage core than the safety temperature threshold for the safety temperature threshold circuit. Thus, in some embodiments, the thermal storage device may be configured such that a build-up of excessive heat in the thermal storage core results in the controller causing the individual circuit breaker circuits to prevent the supply of power to the respective heating elements, with the safety temperature threshold circuit acting as a back-up, fail-safe, function.

[0016] For example, in some embodiments where a maximum design temperature of the thermal storage core is about 1400 °C, or in some embodiments where a maximum design temperature of the thermal storage core and any associated insulation is about 1000 °C , the safety temperature threshold may be at least: 825 °C, 850 °C, 875 °C, or 900 °C. Preferably, the safety temperature threshold may be about 875 °C. Thus, the safety temperature threshold may be set below the maximum design temperature of the thermal storage core to avoid potential overheating of the thermal storage core and to avoid excessive heating of the thermal storage device (and any associated insulation where appropriate) . Where the safety temperature threshold is at least 825 °C, the operational temperature threshold may be set below the safety temperature threshold, for example below 825 °C. For example, an operational temperature threshold may be about 800 °C. As such, the operational temperature threshold may be set at least: 10 °C, 20 °C, 30 °C, 40 °C, 50 °C, or 75 °C below the safety temperature threshold. Thus, the operational temperature threshold may be set to be a primary means of avoiding overheating of the thermal storage core, wherein the safety temperature threshold provides a failsafe back-up. That is to say, in some embodiments, the safety temperature threshold may be set at about at least: 10 °C, 20 °C, 30 °C, 40 °C, 50 °C or 75 °C above the operational temperature threshold.

[0017] In some embodiments, the safety temperature threshold is no greater than: 1400 °C, 1350 °C, 1300 °C, 1200 °C, 1000 °C, 950 °C, 900 °C, or 875 °C. Thus, the safety temperature threshold may be selected to prevent overheating of the thermal storage core.

[0018] In some embodiments, the thermal storage device further comprises a plurality of isolating couplers, preferably opto-couplers, wherein an isolating coupler is connected between the controller and each of the plurality of circuit breaker circuits such that the controller is electrically isolated from the plurality of circuit breaker circuits. As such, isolating couplers may be provided to allow the controller to control the plurality of heating circuits whilst being electrically isolated from the electrical circuit used to power the heating elements. For example, in some embodiments, the plurality of heating elements may each be powered by a relatively high voltage circuit. In some embodiments, the controller may be powered by a low voltage circuit. By connecting the controller to the plurality of circuit breaker circuits, the relatively low voltage circuit powering the controller may be electrically isolated from the relatively high voltage circuit powering the heating elements.

[0019] In some embodiments, the thermal storage device further comprises a power control circuit for each of the heating elements, each power control circuit configured to control the supply of electrical energy to the respective heating element. The thermal storage device may also comprise a controller configured to control the thermal storage device; wherein the controller is configured to control each of the plurality of power control circuits in order to control the supply of electrical energy to each of the plurality of heating elements via the power control circuits. As such, the controller may provide software-based control of the heating elements via the plurality of power control circuits. In some embodiments, each power control circuit may comprise a thyristor. Such non-isolating power control circuits may allow the controller to control the supply of power to the heating elements for normal operation of the thermal storage device. In some embodiments, the controller may also control the plurality of circuit breaker circuits as discussed above in order to be able to isolate one or more heating elements from the supply of electrical energy.

[0020] In some embodiments, the temperature sensor comprises a thermocouple.

[0021] In some embodiments, the thermal storage core comprises magnetite.

[0022] In some embodiments, each circuit breaker circuit comprises a relay.

[0023] In some embodiments, the thermal storage device comprises an additional safety temperature threshold circuit, the additional safety temperature threshold circuit configured to receive the temperature signal from the temperature sensor and / or an additional temperature signal from an additional temperature sensor disposed in the thermal storage core. In some embodiments, the additional safety temperature threshold circuit is configured to output an additional safety temperature signal to the plurality of circuit breaker circuits based on the temperature signal and / or the additional temperature signal and the safety temperature threshold. As such the thermal storage device may be provided with one or more additional safety temperature threshold circuits which may each be configured to perform the same functions as the safety temperature threshold circuit. Thus the thermal storage device may have built in redundancy in order to provide further failsafe functionality.

[0024] In some embodiments, a plurality of temperature sensors may be provided within the thermal storage core, wherein each temperature sensor is configured to output a temperature signal representative of a temperature of the thermal storage core. In some embodiments, each temperature sensor is configured to output a respective temperature signal to the safety temperature threshold circuit. Alternatively, one or more temperature sensors may output a signal to the additional safety temperature threshold circuit. The safety temperature threshold circuit may then be configured to receive the temperature signals and output a safety signal when each temperature signal indicates that a temperature of the thermal storage core is below a safety temperature threshold of the safety temperature threshold circuit. When one or more temperature signals indicate that a temperature of the thermal storage is above a safety temperature threshold of the safety temperature threshold circuit, the safety signal is not output by the safety temperature threshold circuit. By providing a plurality of temperature sensors, preferably evenly spaced apart, or distributed within the thermal storage core, localised hot spots within the thermal storage, should any occur, may be more readily detected by the thermal storage device.

[0025] In some embodiments, the thermal storage device may be configured to be connected to an external heat demand system. For example the thermal storage device may be configured to be connected to a domestic hot water circuit, domestic central heating system or hot air system or any other heat demand system. In some embodiments, the thermal storage device further comprises a heat exchanger configured to transfer thermal energy from the thermal storage core to the external heat demand system.

[0026] According to a second aspect of the disclosure, a thermal storage device is provided. The thermal storage device comprises: a thermal storage core configured to store thermal energy; a plurality of heating elements each configured to heat the thermal storage core; a temperature sensor disposed in the thermal storage core and configured to output a temperature signal representative of a temperature of the thermal storage core; a safety temperature threshold circuit configured to receive the temperature signal and output a safety signal when the temperature signal indicates that a temperature of the thermal storage core is below a safety temperature threshold of the safety temperature threshold circuit; a circuit breaker circuit for the plurality of heating elements, wherein the plurality of heating elements are connected in parallel to the circuit breaker circuit, the circuit breaker circuit configured to allow the supply of electrical energy to plurality of heating elements upon receiving the safety signal from the safety temperature threshold circuit, wherein when the safety signal is not received, the circuit breaker circuit is configured to prevent the supply of electrical energy to the heating elements.

[0027] As such the thermal storage device of the second aspect has a plurality of heating elements connected to a single circuit breaker circuit. By providing a single circuit breaker circuit, the number of circuit breaker circuits may be reduced, wherein the circuit breaker circuit is rated to handle the power draw of the plurality of heating elements.

[0028] It will be appreciated that the thermal storage device of the second aspect may be operated in a similar manner to the thermal storage device of the first aspect. As such, the thermal storage of the second aspect may incorporate any of the optional features discussed above in relation to the first aspect of the disclosure.

[0029] Brief description of the figures

[0030] By way of example only, embodiments of the present disclosure are now described with reference to, and as shown in, the accompanying figures, in which:

[0031] Fig. 1 shows an isometric drawing of a thermal storage device according to an embodiment of the disclosure;

[0032] Fig. 2 shows a cross section of the thermal storage device of Fig. 1;

[0033] Fig. 3 is a block diagram of a safety system of the thermal storage device according to an embodiment of the disclosure;

[0034] Fig. 4 is a block diagram of another safety system of a thermal storage device according to an embodiment of the disclosure; and Fig. 5 is a block diagram of a further safety system of a thermal storage device according to an embodiment of the disclosure.

[0035] Detailed description

[0036] According to an embodiment of the disclosure, a thermal storage device 1 is provided. An isometric drawing of a thermal storage device 1 , including a cut-away portion is shown in Fig. 1.

[0037] As shown in Fig. 1, the thermal storage device 1 comprises a thermal storage core 11. The thermal storage core 11 comprises a medium capable of storing thermal energy, principally by sensible heat storage (or antiferromagnetic and eutectoid transition effects), for extraction at a later time. In some embodiments, the thermal storage core 11 may comprise different heat storage materials. For example in some embodiments, at least approximately 25%, or at least 50% of the volume of the thermal storage core may comprise the same heat storage material. The thermal storage core 11 may comprise an oxidising material and may be solid. Alternatively, the thermal storage core 11 may comprise a phase change material. The thermal storage core 11 may comprise a metal and may comprise at least one of an iron oxide and / or a ferrous metal or iron alloy (preferably with at least 90 wt% or 95 wt% iron content and / or up to 4 wt% carbon content). The iron oxide may comprise magnetite (Fe3O4), hematite (Fe2O3), wustite (FeO) and / or any other suitable iron oxide. Further details of suitable thermal storage cores 11 may be found in at least WO-A-2021037865.

[0038] The core 11 may further comprise a core housing 130 wherein the thermal storage core 11, also called a heat storage medium, is disposed within the core housing 130. The core housing 130 may comprise or define a core chamber 32 within it and in which the thermal storage core 11 is located or dispersed. The core chamber 32 may be a sealed chamber, in particular sealed from the environment external to the thermal storage core 11 and / or thermal storage device 1 such that gas cannot be communicated into or out of the core chamber 32. The core housing 130 preferably comprises a non-oxidising material, such as stainless steel. As illustrated, the core housing 130 may be substantially cuboidal such that the core chamber 32 is also substantially cuboidal and may comprise an open core main housing 34 and a lid 36 to seal the opening of the core main housing 34. The lid 36 may be removable for access to the core chamber 32 for maintenance. However, the core housing 130 and core chamber 132 may have any other suitable shape and / or construction.

[0039] The thermal storage device 11 may also comprise: a base 101, wherein the thermal storage core 11 may be mounted to the base 101; a fluid system 103 extending through the thermal storage core 11 and base 101 for heating a transfer fluid in the thermal storage core 11 and for circulating the heated transfer fluid between the thermal storage core 11 and the base 101. The thermal storage device 1 may further comprise an external heat demand system 105 wherein the fluid system 103 is further configured for extracting the heat from the transfer fluid for supply to the external heat demand system 105. The external heat demand system 105 may comprise a domestic hot water circuit, domestic central heating system or hot air system or any other heat demand system.

[0040] For example, the thermal storage device 10 may be a thermal storage boiler wherein the external heat demand system 105 may comprise a domestic hot water circuit or domestic central heating system, wherein the heat from the transfer fluid is used to heat water.

[0041] The base 101 of the thermal storage device 1 may comprise a base housing 111 defining an internal base chamber through which the fluid system 103 may extend. The base housing 111 may be connected to a base mounting plate 117, provided towards the thermal storage core 11. Fig. 2 shows a further cross-section of the thermal storage device 1 of Fig. 1.

[0042] The thermal storage device 1 may further comprise an insulation arrangement 120 located between and mounted to the base 101 and thermal storage core 11 for insulating the components in the base 101 from the heat of the thermal storage core 11. The insulation arrangement 120 may be mounted to and between the base housing 111, preferably to the mounting plate 117 thereof, and the core housing 130. Preferably the insulation arrangement 120 comprises at least one insulation block comprising a thermal insulating material, for example, calcium silicate or microporous board. Preferably the insulation arrangement 120 encases the thermal storage core 11 on all sides of the thermal storage core 11 (i.e. the insulation arrangement surrounds the thermal storage core 11 on all sides of the thermal storage core 11). As shown in Figs. 1 and 2, insulation passageways 125 may extend through the insulation arrangement 120, preferably entirely therethrough, to allow the communication of fluid between the core 11 and the base 101. In other embodiments the thermal storage core 11 may be mounted directly to the base 101.

[0043] The fluid system 103 defines a fluid circulation circuit for the transfer fluid to circulate between the thermal storage core 11 and the base 101. The fluid system 103 is preferably a closed loop, constant volume system. The transfer fluid is preferably air. The fluid system 103 may comprise a heat exchanger 133 and a fan 135, which may be mounted inside the base 101 , particularly the base housing 111 thereof. The heat exchanger 133 may be located downstream of the thermal storage core 11 and upstream of the fan 135. The heat exchanger 133 is configured to extract heat from the heated transfer fluid and transfer the heat to the heat demand system 105. The heat demand system 105 may comprise, for example, at least one pipe circulating a fluid, such as water or air, through the heat exchanger 133 as shown in Fig. 2. The heat exchanger 133 may be of any suitable type, such as fin and tube, or material, such as brazed copper.

[0044] The fan 135 is configured to direct the transfer fluid around the fluid system 103. The fan 135 may be located upstream of the thermal storage core 11 and downstream of the heat exchanger 133. The fan 135 may comprise a fan inlet (not shown) for receiving cooler transfer fluid from the heat exchanger 133. For example, the fan inlet may be mounted substantially directly at the exchanger outlet (not shown). The fan 135 may comprise a fan outlet 137 out of which it drives transfer fluid towards the fluid system 103 and the thermal storage core 11. The fan 135 may be driven by fan motor 145, such as an electronically commutated (EC) motor. The fan motor 145 may be variable to drive the fan 135 to provide a variable flowrate and thus control the power output from the thermal storage core 11.

[0045] The fluid system 103 further may comprise a cooled fluid passageway 151 extending from the heat exchanger 133 to the core 11 , core fluid passageways 153 extending through the core 11 and a heated fluid passageway 155 extending from the core 11 to the heat exchanger 133. The cooled fluid passageway 151 may diverge into and be connected to the core fluid passageways 153 and the heated fluid passageway 155 may be connected to and converge from the core fluid passageways 153. The cooled and heated fluid passageways 151, 153 may be located in the base 101 and, if present, insulation arrangement 120. Each core fluid passageway 153 may be provided by a fluid conduit through the thermal storage core 11. The fluid conduits extend, preferably entirely and continuously, thermal storage core 11 for enabling the transfer of heat from the thermal storage core 11 , through the fluid conduits and to the transfer fluid in the core fluid passageways 153 by forced convection. The core fluid passageways 153, and the transfer fluid therein, are sealed from the core chamber 32 by, for example, the fluid conduits being sealed and mounted to the core housing 130. As a result, the transfer fluid passes through the thermal storage core 11 without contacting the thermal storage core 11.

[0046] Preferably, the fluid conduits comprise a conductive material such that heat from the thermal storage core can be effectively transferred to the transfer fluid. Preferably the fluid conduits comprise a metal, for example steel, stainless steel, an Incoloy (RTM) alloy or an Inconel (RTM) alloy, or a ceramic, such as silicon carbide. Although not illustrated, the fluid conduits may comprise at least one fin on their exterior walls for improving heat transfer with the thermal storage core 11.

[0047] The thermal storage device 1 may further comprise a controller (not illustrated in Figs. 1 and 2). The controller may communicate with various sensors and actuators of the thermal storage device 1. For example, the controller may be configured to control the operation of the fan motor 145 in order to control the amount of heat transferred from the thermal storage core 11 to the external heat demand system 105. The controller may comprise at least one processor, at least one memory and at least one network adapter for allowing communication between the at least one processor and an external network, such as the Internet. The at least one sensor may comprise the at least one temperature sensor 51. The control system may comprise at least one exchanger temperature sensor located in the heated fluid passageway 155, preferably adjacent to or at the exchanger inlet 137, for determining the temperature of transfer fluid entering the heat exchanger 133. The control system may comprise at least one fan temperature sensor located in the cooled fluid passageway 151, preferably adjacent to or at the fan outlet 137, for determining the temperature of cooled transfer fluid exiting the fan 135. The control system may therefore control the fluid system 103 and electrical system 14 based upon the output from the at least one temperature sensor 51. The control system may also monitor the electrical power consumption of the electrical system 14 and / or the frequency of the electricity grid to which it is connected and use the resulting data to control the time of heating of the core 11.

[0048] During a normal operating mode of the thermal storage device 1 , wherein the temperature of the thermal storage core 11 is below a safety temperature, the controller controls the power supply 24 to supply electrical energy to the heating elements 15a, 15b, 15c. The heating elements 15a, 15b, 15c convert the electrical energy to heat, which is then stored in the thermal storage core 11. The thermal storage core 11 stores the heat therein where it may be used for later extraction by the fluid system 103. By controlling the electrical power received by the heating elements 15a, 15b, 15c, the controller may control the heating of the thermal storage core 11 to an operating temperature range. Thus, if the controller determines that the temperature of the thermal storage core 11 is below the operating temperature range, or below a desired core temperature, the controller causes heating elements 15a, 15b, 15c to heat the thermal storage core 11. If the temperature of the thermal storage core 11 reaches, exceeds or is expected to reach the operating temperature range or desired core temperature, the controller causes the heating elements 15a, 15b, 15c to stop, or to reduce, heating of the thermal storage core 11 controlling the electrical energy provided to the heating elements 15a, 15b, 15c.

[0049] During the normal operating mode of the thermal storage device 1, in order to extract heat from the thermal storage device 10, the controller may operate the fan 135 to circulate transfer fluid around the fluid circulation circuit. The fan 135 directs transfer fluid from the heat exchanger 133 (in which it has been cooled) through the cooled fluid passageway 151 and into the core fluid passageways 153. The transfer fluid is driven through the core fluid passageways 153 in which it receives heat conducted through the fluid conduits from the thermal storage core 11. The heated transfer fluid is then driven from the core fluid passageways 153 through the heated fluid passageway 155 into the heat exchanger 133.

[0050] During the normal operating mode of the thermal storage device 1, the controller may control the power output of the thermal storage device 1 by varying the speed of the fan 135 to control the transfer fluid flowrate through the thermal storage core 11. The controller controls the power output of the thermal storage device 1 at a given core temperature, determined by at least one temperature sensor located in the thermal storage core, by controlling the speed of the fan 135, thereby controlling the transfer fluid flowrate through the thermal storage core 11. In particular, the controller may determine or receive a desired heat power output and / or desired water temperature at the heat demand system 105, for example based upon at least one temperature sensor located in the heat demand system 105 such as at a hot water outlet, and / or a desired transfer fluid flowrate through the core 11 and operate the fan 135 to at least one of a plurality of fan speeds (e.g. selecting one speed from a continuous range of speeds) based upon the desired heat power output, desired water temperature and / or desired transfer fluid flowrate. Hence, when the thermal storage core 11 is at a certain temperature, if less than the maximum power output is required, the speed of the fan 135 is reduced from its maximum.

[0051] The operating temperature range may be a temperature range for the thermal storage core 11. When the thermal storage core 11 is at a temperature within the operating temperature range, the controller determines that the thermal storage device 1 is in the normal operating mode. Accordingly, when the thermal storage core is at a temperature within the operating temperature range, the heating elements 15a, 15b, 15c are able to provide receive electrical power in order to heat to the thermal storage core 11. Additionally, when the thermal storage core 11 is in the operating temperature range, the fluid system 103 may be operated to extract heat from the thermal storage core 11. In some embodiments, the operating temperature range may be from approximately 700 °C to approximately 1150 °C, or more preferably from approximately 700 °C to approximately 800 °C.

[0052] In addition to the controller, which controls the operation of the thermal storage device 1 during a normal operating mode of the thermal storage device 1, the thermal storage device also includes a safety system which prevents excessive heating of the thermal storage core 11. The safety system will now be described with reference to the block diagram shown in Fig. 3. It will be appreciated that the components indicated in Fig. 3 may be arranged at suitable locations in the thermal storage device 1 of Figs. 1 and 2. Like reference numerals are used in Fig. 3 to indicate features shown in Figs. 1 and 2.

[0053] As shown in Fig. 3, the thermal storage device 11 comprises a thermal storage core 11, a temperature sensor 13, a plurality of heating elements 15a, 15b, 15c, a safety temperature threshold circuit 20, and a plurality of circuit breaker circuits 22a, 22b, 22c. As further shown in Fig. 3, the thermal storage device comprises a power supply 24 and a plurality of power control circuits 17a, 17b, 17c. In effect, the safety system for the thermal storage device 1 is provided by the temperature sensor 13, the safety temperature threshold circuit 20, and the plurality of circuit breaker circuits 22a, 22b, 22c as discussed in further detail below.

[0054] The temperature sensor 13 is disposed in the thermal storage core 11 and configured to output a temperature signal representative of a temperature of the thermal storage core. The temperature sensor 13 may comprise a thermocouple. The temperature sensor 13 preferably extends into the thermal storage core 11 as a means to measure the temperature of the thermal storage core. The temperature sensor (thermocouple) may be a Mineral Insulated Thermocouple Insert with DIN Plate (MTD). In some embodiments, the temperature sensor 13 may be a K type duplex sensor.

[0055] The plurality of heating element 15a, 15b, 15c are each configured to heat the thermal storage core 11. In the embodiment of Fig. 3, the heating elements 15a, 15b, 15c receive electricity from the power supply 24 in the form of an alternating current. The heating elements 15a, 15b, 15c may each comprise electrical resistive heating elements for converting electrical power into heat. The heating elements 15a, 15b, 15c preferably comprises electrical elements or coils. The heating elements 15a, 15b, 15c may each extend through the thermal storage core 11. Preferably, each heating element 15a, 15b, 15c is mounted in the thermal storage core 11 inside an electrically nonconductive sheath, which may, for example, comprise ceramic. As such, the heating elements 15a, 15b, 15c may be sealed from the core chamber 32 such that they are not in direct electrical contact with the thermal storage core 11.

[0056] The safety temperature threshold circuit 20 is configured to receive the temperature signal from the temperature sensor 13. The safety temperature threshold circuit is also configured to output a safety signal when the temperature signal indicates that a temperature of the thermal storage core 11 is below a safety temperature threshold of the safety temperature threshold circuit. The safety signal may be a non-zero voltage. For example, in some embodiments, the safety temperature threshold for the thermal storage core 11 may be at least 825 °C. As such, when operational, the safety temperature threshold circuit may be configured to output a signal (e.g. a non-zero voltage) which is indicative that that safety temperature threshold circuit is operational (e.g. it has power), and also that the temperature of the thermal storage core is below the safety temperature threshold.

[0057] Where the temperature signal indicates that a temperature of the thermal storage core 11 is at least equal to the safety temperature threshold, the safety temperature threshold circuit 20 is configured to not output the safety signal. In some embodiments, the safety temperature circuit 20 may output an excessive heat signal which indicates that the temperature of the thermal storage core 11 is at least equal to the safety temperature threshold. In some embodiments, the excessive heat signal may be a zero voltage. As such, in some embodiments an absence of power to the safety temperature threshold circuit 20 may cause the safety temperature threshold circuit to output the excessive heat signal. Thus, the safety temperature threshold circuit 20 may be configured to output the excessive heat signal in the event of a fault in the safety system.

[0058] In some embodiments, the safety temperature threshold circuit 20 may comprise a comparator which is configured to compare the temperature signal (i.e. a voltage representative of the temperature signal) to a safety temperature threshold voltage (i.e. a voltage indicative of the safety temperature threshold). The safety temperature threshold voltage may be provided by a resistive divider. In some embodiments, the resistive divider may comprise one or more variable resistors in order to allow the safety temperature threshold to be adjustable by a manufacturer or installation engineer. The resistive divider may be provided with a range of variable resistance corresponding to an allowable range of safety temperature thresholds. For example, the variable resistor may allow the safety temperature threshold to be set to at least 825 °C and no greater than 1400 °C for example. It will be appreciated that the allowable range for the safety temperature threshold will depend on the maximum design temperature for the thermal storage core 11 and any associated insulation.

[0059] A plurality of circuit breaker circuits 22a, 22b, 22c are provided, one for each of the heating elements 15a, 15b, 15c. In the embodiments of Figs. 1 to 3, three heating elements 15a, 15b, 15c are provided (and thus three circuit breaker circuits 22a, 22b, 22c are provided). Of course, in other embodiments, a different number of heating elements may be provided.

[0060] Each circuit breaker circuit 22a, 22b, 22c is configured to allow the supply of electrical energy to the respective heating element upon receiving the safety signal from the safety temperature threshold circuit 20. When the safety signal is not received by the plurality of circuit breaker circuits 22a, 22b, 22c, each circuit breaker circuit is configured to prevent the supply of electrical energy to the respective heating element 15a, 15b, 15c.

[0061] In some embodiments, each circuit breaker circuit 22a, 22b, 22c comprises a relay. As such, each circuit breaker circuit 22a, 22b, 22c may be configured to electrically isolate the associated heating element 15a, 15b, 15c from the power supply 24 when the safety signal is not received by the circuit breaker circuit 22a, 22b, 22c. Preferably, each relay is a normally open relay, such that the safety signal (of a predetermined voltage) is required to close the relay and allow electrical energy to flow to the associated heating element 15a, 15b, 15c. In the event of a fault (e.g. a power failure), the relay will fail-safe to an open position, preventing the supply of power to the associated heating element 15a, 15b, 15c.

[0062] As shown in Fig. 3, the safety temperature threshold circuit 20 is connected to each of the plurality of circuit breaker circuits 22a, 22b, 22c. Thus, a single safety threshold circuit 20 may be provided to control each of the circuit breaker circuits 22a, 22b, 22c, thereby reducing the cost of the safety system for the thermal storage device 1 . Similarly, a single temperature sensor 13 may be provided to provide the temperature signal for the safety threshold circuit 20.

[0063] It will be appreciated that the temperature sensor 13, safety temperature threshold circuit 20 and the circuit breaker circuits 22a, 22b, 22c may be implemented entirely as discrete electronic components. That is to say, the safety temperature threshold circuit and the circuit breaker circuits 22a, 22b, 22c may be implemented without relying on softwarebased control (e.g. a controller) such that the safety system provides a robust system for preventing excessive heating of the thermal storage core 11 .

[0064] The power supply 24 is configured to supply the heating elements 15a, 15b, 15c with electrical energy when the heating elements 15a, 15b, 15c are to be used to generate heat. The power supply 24 of the thermal storage device may be connected to external power source (not illustrated), such as an electricity grid or network or power station. In some embodiments the power supply 24 may be connected to a local power source, such as a generator, renewable energy source (e.g. a solar panel (solar cell), wind turbine) or any other device capable of supplying the heating elements 15 with electrical power. In the embodiment of Fig. 3, the power supply 24 provides alternating current (e.g. at a mains electrical voltage, e.g. 230 V or 110 V) to the heating elements 15a, 15b, 15c via the circuit breaker circuits and the power control circuits 17a, 17b, 17c.

[0065] The power control circuits 17a, 17b, 17c are each configured to allow a controller (not shown) to control the flow of electrical energy from the power supply 24 to the associated heating element. As such, each power control circuit 17a, 17b, 17c is configured to control the supply of electrical energy to the associated heating element. For example, in the embodiment of Fig. 3, each power control circuit 17a, 17b, 17c comprises a thyristor (e.g. a TRIAC) or other suitable semiconductor switching device / circuit (e.g. a Metal Oxide Semiconductor Field Effect Transistor or Insulated Gate Bipolar Transistor and any associated driving circuitry), wherein the gate of the thyristor is connected to the controller. Thus, the controller can output a control signal to the gate of the thyristor in order control the flow of electrical energy through the thyristor.

[0066] Thus, in use, the plurality of circuit breaker circuits 22a, 22b, 22c of the thermal storage device 1 allow electrical energy to flow from the power supply 24 to the power control circuits 17a, 17b, 17c providing that the safety signal is received from the safety temperature threshold circuit 20. If the safety signal is not received by the plurality of circuit breaker circuits 22a, 22b, 22c, each of the circuit breaker circuits 22a, 22b, 22c is configured to electrically isolate the power control circuits 17a, 17b, 17c (and thus the heating elements 15a, 15b, 15c) from the power supply 24. For example, the plurality of circuit breaker circuits 22a, 22b, 22c may each comprise a “normally open” relay in order to provide the desired isolating functionality.

[0067] In some embodiments, the controller may also be provided with additional functionality to isolate one or more of the heating elements. For example, Fig. 4 provides a block diagram of such an embodiment.

[0068] In the embodiment of Fig. 4, a controller 30 is provided. The controller 30 is configured to control the thermal storage device 1 as discussed above for the embodiments of Figs. 1 to 3. Thus, as shown in Fig. 4, the controller 30 is configured to control each of the power control circuits 17a, 17b, 17c in order to control the heating of the heating elements 15a, 15b, 15c under normal operation.

[0069] Additionally, as shown in Fig. 4 the controller 30 is configured to control each of the plurality of circuit breaker circuits 22a, 22b, 22c in order to control the supply of electrical energy to each of the plurality of heating elements 15a, 15b, 15c in addition to the safety temperature threshold circuit 20. That is to say, each of the controller 30 and the safety temperature threshold circuit 20 may cause each of the plurality of circuit breaker circuits to electrically isolate the associated heating element 15a, 15b, 15c from the power supply 24.

[0070] In the embodiment of Fig. 4, the controller 30 may control each of the plurality of circuit breaker circuits 22a, 22b, 22c individually in order to provide the option of electrically isolating some, but not all of the heating elements 15a, 15b, 15c. It will be appreciated that in the embodiment of Figs 3 and 4, the safety temperature threshold circuit 20 provides the same safety signal (or excessive heat signal) to each of the circuit breaker circuits 22a, 22b, 22c. Thus, the controller 30 may be used to provide individual isolation of a heating element 15a, 15b, 15c without changing the functionality of the safety temperature threshold circuit 20. As such, the controller 30 may be used to isolate a heating element 15a, for example due to a fault with heating element 15a, whilst allowing the other heating elements 15b, 15c to remain operational.

[0071] Thus, in some embodiments, the controller 30 is configured to determine an operational state or a non-operational state of each of the plurality of the heating elements 15a, 15b, 15c. Upon determining the non-operational state for one or more of the heating elements, 15a, 15b, 15c the controller 30 is configured to control the circuit breaker circuits associated with the one or more heating elements having the non-operational state to cause said circuit breaker circuits to prevent the supply of electrical energy to the associated one or more heating elements. For example, the controller 30 may determine a non-operational state for one or more of the plurality of heating elements 15a, 15b, 15c based on an input from a heating engineer, based on a measured current or voltage reading from the heating element (e.g. a short or open circuit associated with the heating element) or any other criteria indicative of a fault with the heating element 15a, 15b, 15c.

[0072] In some embodiments, the controller 30 may be configured to determine a temperature associated with each of the heating elements 15a, 15b, 15c and to obtain an operational temperature threshold associated with each of the heating elements. For example, the thermal storage core 11 may be provided with additional temperature sensors (not shown in Fig. 4) which are located in the thermal storage core 11. Each additional temperature sensor may be associated (e.g. located proximal to) a heating element 15a, 15b, 15c. As such, each additional temperature sensor may be configured to determine the local temperature of the thermal storage core 11 around the associated heating element. Alternatively, the temperature sensor 13 may be used to determine the temperature associated with each of the heating elements 15a, 15b, 15c.

[0073] The controller 30 may be configured to determine an operational state or a non-operational state of each of the plurality of heating elements 15a, 15b, 15c based on the temperature associated with the respective heating element (e.g. the local temperature of the thermal storage core 11 determined by the additional temperature sensors) and the operational temperature threshold for the associated heating element 15a, 15b, 15c. As such, the controller 30 may provide an additional, software-based safety control system for each of the heating elements 15a, 15b, 15c.

[0074] Preferably, in some embodiments, the operational temperature threshold associated with each of the plurality of the heating elements 15a, 15b, 15c is lower than the safety temperature threshold of the safety temperature threshold circuit 20. For example, the operational temperature threshold may be at least: 10 °C, 20 °C, 30 °C, or 50 °C below the safety temperature threshold. For example, the operational temperature threshold may be about 800 °C and the safety temperature threshold may be about 825 °C or 850 °C. Thus, in some embodiments, excessive local heating of the thermal storage core 11 may initially prompt the controller 30 to electrically isolate one or more heating elements 15a, 15b, 15c from the power supply. Where the temperature of the thermal storage core 11 continues to rise, the safety temperature threshold provided by the safety temperature threshold circuit 20 provides an additional fail-safe circuit which is configured to electrically isolate the heating elements 15a, 15b, 15c.

[0075] In some embodiments, as shown in Fig. 4, the controller 30 is connected to each of the circuit breaker circuits via an isolating coupler 32a, 32b, 32c, preferably an opto-coupler. Thus, as shown in Fig. 4 an isolating coupler is connected between the controller 30 and each of the plurality of circuit breaker circuits 22a, 22b, 22c, such that the controller 30 is electrically isolated from the plurality of circuit breaker circuits 22a, 22b, 22c. Thus, the voltages used to power the controller 30 (typically a relatively low voltage) may be electrically isolated from the power supply 24 used to power the heating elements 15a, 15b, 15c.

[0076] In a further embodiment, the thermal storage device may be provided with an additional safety temperature threshold circuit 20a to provide a redundant fall-back safety system for the thermal storage device 1. The additional safety temperature threshold circuit 20a may be configured to receive the temperature signal from the temperature sensor 13 and / or an additional temperature signal from an additional temperature sensor 13a (e.g. as shown in Fig. 5) disposed in the thermal storage core 11.

[0077] The additional safety temperature threshold circuit 20a may be configured to output an additional safety temperature signal to the plurality of circuit breaker circuits 22a, 22b, 22c based on the temperature signal and / or the additional temperature signal and the safety temperature threshold. As such, the additional safety temperature threshold circuit 20a may perform the same functionality as the safety temperature threshold circuit 20. In the embodiment of Fig. 5, where the circuit breaker circuits 22a, 22b, 22c, do not receive the safety signal from both the safety temperature circuit 20 and the additional safety temperature circuit 20a, the circuit breaker circuits 22a, 22b, 22c act to electrically isolate the heating elements 15a, 15b, 15c from the power supply 24. That is to say, if the circuit breaker circuits 22a, 22b, 22c receive an excessive heat signal from either of the safety temperature threshold circuit 20 or the additional safety temperature threshold circuit 20a, the circuit breaker circuits 22a, 22b, 22c act to electrically isolate the heating elements 15a, 15b, 15c from the power supply 24.

Claims

CLAIMS:

1. A thermal storage device comprising: a thermal storage core configured to store thermal energy; a plurality of heating elements each configured to heat the thermal storage core; a temperature sensor disposed in the thermal storage core and configured to output a temperature signal representative of a temperature of the thermal storage core; a safety temperature threshold circuit configured to receive the temperature signal and output a safety signal when the temperature signal indicates that a temperature of the thermal storage core is below a safety temperature threshold of the safety temperature threshold circuit; a circuit breaker circuit for each of the plurality of heating elements, each circuit breaker circuit configured to allow the supply of electrical energy to the respective heating element upon receiving the safety signal from the safety temperature threshold circuit, wherein when the safety signal is not received, each circuit breaker circuit is configured to prevent the supply of electrical energy to the respective heating element.

2. A thermal storage device according to claim 1, further comprising a controller configured to control the thermal storage device, wherein the controller is configured to control each of the plurality of circuit breaker circuits in order to control the supply of electrical energy to each of the plurality of heating elements in addition to the safety temperature threshold circuit.

3. A thermal storage device according to claim 3, wherein the controller is configured to determine an operational state or a non-operational state of each of the plurality of the heating elements, wherein upon determining the non-operational state for one or more of the heating elements, the controller is configured to control the circuit breaker circuits associated with the one or more heating elements having the non-operational state to cause said circuit breaker circuits to prevent the supply of electrical energy to the associated one or more heating elements.

4. A thermal storage device according to claim 3, whereinthe controller is configured to determine a temperature associated with each of the heating elements and to obtain an operational temperature threshold associated with each of the heating elements, wherein the controller is configured to determine an operational state or a non- operational state of each of the plurality of heating elements based on the temperature associated with the respective heating element and the operational temperature threshold for the associated heating element.

5. A thermal storage device according to claim 4, wherein the operational temperature threshold associated with each of the plurality of the heating elements is lower than the safety temperature threshold of the safety temperature threshold circuit.

6. A thermal storage device according to any of claims 2 to 5, further comprising a plurality of isolating couplers, preferably opto-couplers, wherein an isolating coupler is connected between the controller and each of the plurality of circuit breaker circuits such that the controller is electrically isolated from the plurality of circuit breaker circuits.

7. A thermal storage device according to any of claims 1 to 6, further comprising: a power control circuit for each of the heating elements, each power control circuit configured to control the supply of electrical energy to the respective heating element; and a controller configured to control the thermal storage device; wherein the controller is configured to control each of the plurality power control circuits in order to control the supply of electrical energy to each of the plurality of heating elements via the power control circuits.

8. A thermal storage device according to any of claims 1 to 7, wherein the temperature sensor comprises a thermocouple.

9. A thermal storage device according to any of claims 1 to 8, wherein the thermal storage core comprises magnetite.

10. A thermal storage device according to any of claims 1 to 9, wherein each circuit breaker circuit comprises a relay.

11. A thermal storage device according to any of claims 1 to 10, further comprising an additional safety temperature threshold circuit, the additional safety temperature threshold circuit configured to receive the temperature signal from the temperature sensor and / or an additional temperature signal from an additional temperature sensor disposed in the thermal storage core, wherein the additional safety temperature threshold circuit is configured to output an additional safety temperature signal to the plurality of circuit breaker circuits based on the temperature signal and / or the additional temperature signal and the safety temperature threshold.

12. A thermal storage device according to any of claims 1 to 11 , wherein the safety temperature threshold is at least 500 °C, preferably at least 600 °C, more preferably at least 800 °C; and / or the safety temperature threshold is no greater than 1400 °C.

13. A thermal storage device according to any of claims 1 to 12, wherein the thermal storage device is configured to be connected to an external heat demand system, the thermal storage device further comprising: a heat exchanger configured to transfer thermal energy from the thermal storage core to the external heat demand system.

14. A thermal storage device according to any of claims 1 to 13, wherein, a plurality of temperature sensors are provided within the thermal storage core, each temperature sensor being configured to output a temperature signal representative of a temperature of the thermal storage core.

15. A thermal storage device according to claim 14, wherein each temperature sensor is configured to output a respective temperature signal to the safety temperature threshold circuit, and the safety temperature threshold circuit is configured to: receive the temperature signals; output a safety signal when each temperature signal indicates that a temperature of the thermal storage core is below a safety temperature threshold of the safety temperature threshold circuit; andwhen one or more temperature signals indicate that a temperature of the thermal storage core is above the safety temperature threshold of the safety temperature threshold circuit, to not output by the safety temperature threshold circuit.

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