Patent Description:
There are numerous instances where a volume of fluid is stored for heating applications with end-use temperature requirements such as domestic hot water provision, space heating or cleaning. In many such applications it is useful to know how much thermal energy there is along with the associated temperature distribution. In the case of domestic hot water, knowing the temperature distribution throughout the vertical extent of the reservoir enables one to compute the useful volume of fluid according to Equation <NUM>, <MAT> where Vuseful is the volume of mixed fluid from a mixed outlet, A is the horizontal cross-sectional area of the fluid storage vessel containing a stratified body of fluid some of which exists at a temperature above Tthresh beneath which the fluid is too cold for direct use, for example as a hot water source. T(γ) is the temperature distribution along a (typically horizontal) y-axis within the vessel with height h. The temperature of the fluid at an inlet of the vessel is denoted by Tc. The mixed fluid is delivered from a mixing valve which takes a flow of fluid from a cold inlet and hot outlet. The temperature distribution needs to be measured for the purposes of the above calculation. The threshold temperature, Tthresh, may often be associated with the thermocline within a stratified body of fluid. A thermocline is an abrupt temperature gradient in a body of water, the layer above having a different temperature from the layer below. The position of the thermocline can be used to infer the quantity of available hot water, in the case of the hot water forming a distinct top layer. The thermocline can be used to determine the useful potential associated with a quantity of thermal energy.

Cooling with heat exchange temperature requirements, such as cold storage, is often used in refrigeration and air-conditioning applications. A vessel containing chilled brine may be used in an industrial process which requires removal of waste heat. Within a stratified vessel of cold fluid, such as brine, the useful or cooling potential of fluid, defined as the volume of coolant, Vuseful (cooling) or waste heat brought to a threshold temperature, is expressed by Equation <NUM>, <MAT> where Tthresh refers to the desired temperature below which is waster heat in the system, T(γ) is the temperature distribution throughout the stored coolant, A is the cross-sectional area of the vessel and Th is the initial temperature of the fluid to be cooled. Equation <NUM> applies to a vessel of water stored above the transition temperature associated with a change in correlation between water density and temperature for a particular operating pressure, typically <NUM>-<NUM>, or more preferably <NUM>-<NUM>, at <NUM>-<NUM> bar, or more preferably at <NUM>-<NUM> bars.

Knowing the useful heating or cooling volume can enable determination of the approximate position of the thermocline within the vessel. Where a tank contains hot water for potable or bathing applications, temperatures beneath the lowest heating point are often insufficient to ensure full sterilisation of human pathogens such as Pseudomonas, Legionella, E. Coli, etc. This situation arises due to the fact that conductive heat transfer through water in a tank is significantly slower than the rate of convective heat transfer that arises above an immersion element or heat exchanger. Since this leads to a portion of water within a tank that may host pathogens, a risk arises to the user whenever the tank is drained past the thermocline position (for example the shower going cold when the hot water runs out) as the user may then be exposed to unsanitary water. A system which monitors the position of the thermocline can therefore make the user aware of both the available volume of hot water along with the risk of exposure to unsanitary water. Furthermore, such a system can intervene to minimise such risks by ensuring that the distance between the hot water tank outlet and thermocline is kept above a minimum distance at all times in dependence of the usage profile of the system.

There are a number of sensors that attempt to monitor the thermal energy content within a vessel.

One such example comprises a mechanical water level sensing arrangement operating alongside a means of measuring the electricity consumption of a heating element. However, a mechanical approach is compromised by moving parts, fouling and cost.

An alternative comprises a single thermistor detector. Single temperature measurement may provide an indication of a full tank. However, ignorance of a temperature distribution throughout a vessel prevents a user from determining the remaining quantity of useful heat or cooling potential.

A further alternative comprises a plurality of temperature sensors. A plurality of temperature sensors results in a compromise between the accuracy of measurement (governed by number density of temperature sensors) and the cost and complexity associated with monitoring multiple channels simultaneously.

Further still, an alternative sensor comprises a resistive strip made up of a string of thermistors. A string of Positive Temperature Coefficient (PTC) or Negative Temperature Coefficient (NTC) thermistors can resolve the average temperature within a vessel. However, knowing only the average temperature within the vessel is insufficient in determining the useful volume above a particular threshold temperature. Furthermore, the response of a PTC string is non-linear resulting in large error compared with an ideal response. A string of NTCs is not well suited to resolve the lower limit of the integral in Equation <NUM> and <NUM>, resulting in a lack of knowledge of the threshold temperature above which useful energy (also referred to as exergy) content exists.

<CIT> describes a tank with a sensor system that provides temperature sensors connected in series in a sensor chain. <CIT> describes a bandage that incorporates sensor arrays to estimate a person's core body temperature. <CIT> describes lengths of flexible ribbon or tape or sheets of temperature responsive flexible film or foil that can be applied to a surface from which local regions of variable temperature are to be determined.

According to the present invention, there is provided a sensor for measuring temperature of a fluid within a vessel according to claim <NUM>.

Further features of the invention are characterised by the dependent claims.

Preferably, the elements of the array are coupled in a chain.

Preferably, an aggregate value of the temperature-dependent parameter is indicative of thermal energy content of the fluid in the vessel.

Preferably, the aggregate value of the temperature-dependent parameter has a predetermined relationship to the thermal energy content of the fluid in the vessel.

Preferably, at least one of the elements of the array is configured such that the temperature-dependence of the temperature-dependent parameter is at or near a maximum or minimum at or near a temperature that is a threshold temperature between a useful temperature of the fluid and a non-useful temperature of the fluid.

The temperature-dependent parameter may be resistance, impedance, inductance and/or capacitance.

The elements of the array may be coupled together in series or parallel.

The elements of the array may comprise at least one thermistor.

At least one of the elements of the array may comprise a Positive Temperature Coefficient resistor and/or a Negative Temperature Coefficient resistor and/or a fixed value resistor.

At least one of the elements of the array may comprise a fixed value resistor connected in parallel with a Positive Temperature Coefficient resistor and/or a fixed value resistor connected in parallel with a Negative Temperature Coefficient resistor.

At least one of the elements of the array may comprise a Positive Temperature Coefficient resistor connected in parallel with a Negative Temperature Coefficient resistor and in series thereto a fixed value resistor.

Preferably, the Positive Temperature Coefficient resistor and/or Negative Temperature Coefficient resistor is a non-linear resistor.

The elements of the array may comprise at least one electronic filter circuit, including, but not exclusive to, RC, RL and RLC circuits. Preferably, each element of the array has a predetermined and unique cut-off frequency, preferably at a pre-determined temperature.

Preferably, the sensor is arranged such that selective interrogation of elements of the array can be achieved by exploiting (or using), the unique cut-off frequency of the elements of the array, preferably to determine an interrogated cut-off frequency. Preferably the sensor is arranged to be selectively interrogated by the driving source by applying a frequency sweep around the unique cut-off frequency.

Preferably, the sensor is arranged such that selective interrogation of elements of the array comprises finding an interrogated cut-off frequency or measurement of a temperature dependent parameter.

Preferably, the selective interrogation of elements of the array comprises finding an interrogated cut-off frequency wherein the temperature-dependent parameter is the interrogated cut-off frequency and wherein the relationship between the predetermined cut-off frequency and interrogated cut-off frequency is used to determine a measure of temperature.

Preferably, the relationship between predetermined and interrogated cut-off frequency is indicative of a temperature.

Preferably, the temperature dependent resistance of a thermistor is indicative of a temperature.

The elements of the array may comprise at least one RLC circuit. Preferably, each element of the array has a predetermined and unique resonant frequency, preferably at a predetermined, temperature and the sensor is arranged to find the resonant frequency.

Preferably, the sensor is arranged to be selectively interrogated in order to find an interrogated resonant frequency of interrogate elements of the array to find the resonant frequency. Preferably the relationship between predetermined and interrogated resonant frequency is indicative of a temperature.

Preferably, the relationship between predetermined and interrogated resonant frequency is indicative of a temperature.

Preferably, the relationship between predetermined and interrogated resonant frequency, indicative of temperature, further indicates the thermal energy content of the fluid in the vessel.

Preferably, the detector is arranged to derive the thermal energy content of the fluid in the vessel from the relationship between the predetermined and interrogated resonant frequencies.

The elements of the array may comprise at least one semiconducting device.

Preferably, the semiconducting device element of the array is biasable to enable manipulation of the threshold temperature.

A substrate can provide support and enable manipulation of the array so as to enable cutting.

Preferably, the substrate comprises a pipe. A pipe can provide a simple and economical substrate that shelters and protects the array and provides support.

Preferably, the substrate comprises an adhesive tape. This can enable fixation of the array to a vessel wall. Alternatively, the substrate may comprise a flexible strip or flexible circuit board.

Preferably, the sensor is arranged within a vessel or externally to the vessel.

The elements of the array may be non-uniformly distributed along the length of the sensor array according to sensing requirements.

These and other aspects of the present invention will become apparent from the following exemplary embodiments that are described with reference to the following figures in which:.

<FIG> shows a fluid temperature controller <NUM> comprising a first input for receiving a first signal <NUM> indicating a measurement of an aggregate of a temperature-dependent parameter from a sensor <NUM> within or adjacent a vessel <NUM> (for example, on an interior or exterior wall of the vessel) containing a fluid, either liquid or gas, having a temperature profile. The fluid temperature controller <NUM> has a second input for receiving a second signal <NUM> indicating a temperature of the fluid in the vessel. A processor <NUM> in communication with the controller is configured to calculate thermal energy of the fluid in the vessel based on the first and second signals. A linear exergy sensor is therefore provided.

The processor <NUM> is further configured to determine a volume of useful fluid in the vessel based on the first signal <NUM> and second signal <NUM> and a predetermined threshold temperature between a useful temperature of the fluid and a non-useful temperature of the fluid. The processor of the controller computes the useful volume of fluid available in the vessel <NUM>. The computation by the processor can be according to an equation similar in form to Equation <NUM> or <NUM>. If the sensor <NUM> performs according the Equation <NUM> or <NUM>, then the processor can apply signal conditioning to compute the useful volume of fluid available in the vessel <NUM>. The sensor <NUM> is therefore a linear exergy sensor and the linear exergy sensor provides a signal that provides weight to the useful energy above the threshold temperature (rather than a binary indication beyond a useful temperature).

The processor <NUM> is configured to provide an output control signal to the controller <NUM>, which in turn produces an output <NUM> that regulates a thermal source <NUM> (e.g. a heating element in the case of an electric system) so as to change the temperature of the fluid in the vessel. The controller determines whether the proximity of the thermocline to the vessel outlet <NUM> is such that there is an insufficient useful amount of volume of fluid and thus a risk of a user <NUM> being exposed to fluid which is at an insufficient temperature. Furthermore, the controller aims to prevent a user from being exposed to pathogenic bacteria that could dwell beneath the lowest thermal injection point (in the illustrated example the thermal source <NUM>), whilst at the same time minimising standing heat losses. If such sanitary risks arise on a regular basis, the controller <NUM> can arrange for additional thermal energy to be added as a preventative measure in advance.

The fluid proceeds along the fluid outlet <NUM> whereupon it is mixed with fluid from a cold inlet <NUM>, the output of which is regulated by a mixing valve <NUM>, and the fluid emerges in a mixed outlet <NUM>. The fluid in the vessel <NUM> is replenished through a cold inlet <NUM>. A temperature profile extends between the cold (inlet) region in the vessel <NUM> and the hot (outlet) region in the vessel <NUM>. The temperature profile may exhibit a distinct thermocline, or it may exhibit a gradual transition.

The output control signal that the processor <NUM> provides to the controller <NUM> is subject to approval from or adaptation by a network stress monitor <NUM>. The network stress monitor <NUM> can modify the output control signal in dependence on factors that relate to the network stress. For example, the supply voltage, supply frequency data, or data communications from the supply provider <NUM> can provide information relating to the network stress. Optionally or alternatively the controller <NUM> can interact with the supply provider <NUM> to affect dispatch of energy based on network stress information, and so enable dispatch of energy to the vessel according to availability of energy in the vessel and the cost of energy.

The processor <NUM> can relate cyclic changes in output from the sensor <NUM>, for example over a <NUM>-hour period, to determine, in addition to other parameters such as energy costs, user input <NUM>, user <NUM> requirements, the optimal timing associated with any thermal inputs or outputs from a vessel <NUM> containing a fluid, distribution in network voltage and/or grid frequency as determined by the network stress monitor <NUM>. An adaptive Markov model, or similar statistical approach, could run on the controller and adjust probability weightings assigned to future draw events based on previous draw events and their associations with particular activities (for example the probability of a shower within an hour after a user has drawn a bath) along with the time of day. The Markov model predicts the most likely future demand to allow an algorithm to establish the optimal dispatch of power to immersion elements. A machine-learning process is used to optimally schedule heating of fluid within the vessel according to use of the fluid in the vessel.

The fluid temperature controller <NUM> is able to output information <NUM> regarding the quantity of fluid above (in the case of hot fluid applications) a useful temperature in addition to its mixing potential to the user <NUM>.

The signal from the sensor <NUM> is supplemented by an additional temperature sensing input to yield absolute temperature readings <NUM> in order to normalise the response of the sensor during cyclical operation.

In one embodiment, the sensor <NUM> is immersed within the fluid inside the vessel <NUM>. The sensor <NUM> can be in contact with the vessel wall <NUM>, hence providing an indication of the temperature distribution. In this case, the sensor <NUM> can be fixed to the inner or outer surface of the vessel wall <NUM>.

<FIG> illustrates a mechanical arrangement whereby a protrusion from a sensor-pipe interface <NUM> from a section of pipe <NUM> clears (via an optional step) the flange recess shoulder <NUM>. For vessels with horizontal outlet connections, the protrusion <NUM> bends through <NUM>° before continuing down towards the bottom or up towards the top of the vessel. The circuitry associated with the sensor is embedded in the sensor strip <NUM>. The wiring associated with the sensor is embedded in the sensor strip, protrusion <NUM> and pipe <NUM> wall prior to emerging as the connecting wire <NUM> carrying the sensor output <NUM>. The wire <NUM> terminates at a suitable connector, for example, a two or more pinned connector. The sensor-pipe interface <NUM> connects to the tank flange <NUM> and fluid distribution system via compression, push-fit, bolted flange or any other appropriate arrangement <NUM>. <FIG> illustrates a mechanical arrangement for vessels with vertical connections. The sensor <NUM> protrudes vertically from the sensor-pipe interface <NUM> into the vessel, with no bend. <FIG> show ¾ inch British Standard Pipe (BSP) external threaded compression fittings, which are exemplary fittings that are commonly found in UK domestic hot water systems.

<FIG> show sensors <NUM> with Thermocline Edge Detectors (TEDs) <NUM>. Each TED <NUM> is an element in an array of similar elements. In <FIG> TEDs <NUM> are connected in series. In <FIG> TEDs <NUM> are connected in parallel, where the individual TEDs <NUM> can act as shunts. The TEDs <NUM> are such that the sensor's temperature response follows Equation <NUM> or <NUM> (whether or not a temperature profile exhibits a thermocline). The TEDs <NUM> have a temperature-dependent parameter that gives rise to a temperature response, e.g. changes in resistance or AC impedance. The resistance, impedance or rise time for a temperature-dependent RC network is inferred by: applying a fixed voltage across the sensor terminals; applying a known frequency across the sensor electric terminals <NUM>; injecting a known current through the sensor; or monitoring the response to an impulse or any other arbitrary input function of current or voltage over time. A measure of impedance is made at terminals <NUM>; this is achieved by wiring the network to a fixed resistor with known reference voltage and recording the voltage across the terminals <NUM> as in a voltage divider circuit, or through measurement of a voltage drop on application of a known constant current.

Any number of TEDs <NUM> can be arranged in a series or parallel chain to provide indication of the total thermal energy in the vessel. The positioning and spacing of the TEDs <NUM> within the sensor strip <NUM> can vary according to sensing requirements. For example, a higher resolution is required close to the vessel outlet <NUM> to determine thermocline position with greater accuracy and thus potential sanitary risk to a system user.

Whilst independent wiring of TEDs <NUM>, PTC thermistor or NTC thermistor arrays provides the most accurate resolution of useful volume, this approach also requires multiple electrical connections and channels within the signal conditioning arrangement. The sensors <NUM> described here require a single measurement channel reducing cost and complexity whilst improving reliability. The linear exergy sensor therefore feeds one signal to the control unit from the network of thermosensitive elements. In addition, for the output of sensors wherein resistance is exploited as the temperature-dependent parameter used to indicate useful volumes of fluid, only gain and bias requirements are imposed on signal conditioning, whereas some form of numerical integration of the output of an independent array is required for the same purpose increasing the complexity of any algorithm making the measurement.

<FIG> shows a circuit diagram of a sensor <NUM> comprised of an array of TEDs <NUM> connected in series. <FIG> shows a sensor <NUM> with an array of the same TEDs <NUM> as <FIG>, but with the TEDs <NUM> connected in parallel. Each illustrated TED <NUM> comprises three elements: a thermistor <NUM> in parallel to a resistive element <NUM> and in series thereto a resistor <NUM>. The elements within a TED <NUM> can act as shunts. The thermistor <NUM> can be a PTC or NTC thermistor. The resistive element <NUM> is shown as a resistor, but it can alternatively be a PTC or NTC thermistor or another resistive element. The resistor <NUM> can be omitted.

The resistance of networks such as in <FIG> is inferred via current measurement with constant voltage or voltage measurement with constant current. The current drawn by the sensor for a fixed voltage corresponds to an aggregate of temperature-dependent resistance of the TEDs, which corresponds with the useful volume once the appropriate signal conditioning has been applied. The aggregated temperature-dependent resistance is a cumulative summation of the resistance of the elements (or a selection of the elements) of the sensor array.

<FIG> shows the temperature dependence of the resistance of a TED. The ideal resistance curve <NUM> (dashed line) represents an ideal TED with constant resistance up until the Curie temperature <NUM> of the thermistor; above the Curie temperature <NUM>, the resistance increases linearly with temperature. A typical resistance curve <NUM> (black solid line) of a real-world thermistor is not linear, nor is there a distinct transfer from a constant-resistance regime to a linear-increasing regime. A TED circuit designed to approximate the ideal resistance curve <NUM> has a PTC thermistor in parallel with a fixed value resistor. The TED circuit curve <NUM> (grey solid line) of this circuit behaves significantly more closely to the ideal curve <NUM> than does the thermistor on its own (typical thermistor curve <NUM>). For a TED with an NTC thermistor an ideal resistance curve <NUM> (dashed line) is also shown, and the typical real-world thermistor resistance curve and TED circuit curve are analogous to the illustrated PTC curves. For applications where an upper threshold temperature is relevant (in addition to the lower threshold of the Curie temperature <NUM> as described above), a curve with an upper temperature threshold, after which the resistance remains constant again, can be implemented, analogous to the illustrated curves.

The sensor <NUM> in <FIG>, comprising a chain of TEDs <NUM> connected in series, applied to determining the useful volume of hot fluid within a vessel, solves Equation <NUM> numerically by scaling and biasing the change in terminal resistance of the thermocline sensor according to Equation <NUM>, <MAT>.

For a given TED, index n, the temperature-dependent resistance, represented by RTED(T), is only effective above the component's Curie temperature. Therefore, the cumulative resistance on the right-hand side of Equation <NUM> only includes temperature-dependence associated with TEDs immersed at a temperature above the Curie transition temperature. The Curie transition temperature is selected to coincide with the thermocline transition temperature of interest and thus sets Tthresh. For T(γ) < Tthresh, RTED(T) ≠ <NUM>, so the bias term, Nβ, is required, where N is the total number of TEDs and β is the asymptote resistance for RTED(T < Tthresh). The gain term, K, scales RTED(T) back to T(γ) and in addition includes the term A/Tthresh. For the parallel arrangement of TEDs <NUM> shown in <FIG>, the useful volume of hot fluid within a vessel is solved by Equation <NUM> manipulated to account for the manner in which a parallel configuration of TEDs accumulates resistance. The thermistor elements provide an integral limit above a specified threshold temperature.

For determining a useful volume of coolant within a vessel, the sensors <NUM> illustrated in <FIG> are comprised of TEDs where the thermistors <NUM> alternate along the sensor between PTC and NTC functionality. This arrangement numerically solves Equation <NUM> and can therefore be used to determine a useful volume of coolant below a threshold temperature. The sensor accuracy can be further improved by using an NTC thermistor parallel to a PTC thermistor instead of a fixed resistor parallel to a PTC or NTC thermistor.

An ideal TED responds to temperature transition across a threshold with an instantaneous transition from the temperature-independent regime to the temperature-dependent regime at a temperature associated with the thermocline transition temperature. In practice a TED may not display an abrupt change from the temperature-independent regime to the temperature-dependent regime, but instead displays a departure from the ideal function resulting in a function departure error. The presence of the parallel resistor <NUM> ensures that there is a linear response to temperature beyond the thermistor's Curie transition point. This helps create a more abrupt transition in resistance and manifests itself as a lower function departure error from the ideal function when the temperature of a particular section of the network crosses the threshold temperature. Without a parallel resistive element <NUM> the function departure error becomes very large and traverses a wide range of temperatures when compared with the response for a sensor inclusive of a resistive element <NUM> parallel to a PTC or NTC. Preferably a resistive element is connected in parallel to each TED to minimise the function departure error.

A benefit of a sensor comprising TEDs coupled in parallel is that any number of TEDs can be integrated into a strip which can be cut to the appropriate length or number of TEDs without loss of function to enable easy retrofit for a given installation. The controller <NUM> can be calibrated to a variety of sensor cut lengths either by having the corresponding response preprogrammed for a given length, or by normalising the sensor output to a known reference state such as a fully heated or fully cold vessel of fluid.

The controller is capable of conditioning the resistance measurement such that a variable describing the quantity of useful energy remaining in a vessel is available. A parameter indicative of total thermal exergy within the vessel is therefore obtained.

<FIG> illustrates a sensor comprising a further example of a resistive temperature reactive network <NUM> that solves Equation <NUM> or <NUM> for the purposes of determining the useful heating or cooling fluid volume within a vessel in a discretised manner with no more than two electrical terminals <NUM>.

<FIG> shows an alternative arrangement for a sensor <NUM> with a parallel arrangement of TEDs <NUM>, each TED comprising a capacitor <NUM> in series with a temperature-dependent resistive element <NUM>, thus forming an RC high-pass filter circuit. A sensor comprised of a serial configuration of RC-based TEDs is equally suitable. Throughout the TEDs in the sensor array, capacitors are selected to possess unique value capacitances, with the positions of particular unique value capacitances defined. Along the array identical NTC resistors are used. Therefore each TED possesses a unique predetermined cut-off frequency associated with the RC filter.

Selective interrogation of capacitive TEDs is achieved by driving the sensor with a sine wave signal at a low enough frequency such that the highest value capacitor (also associated with the RC circuit with the lowest cut-off frequency) behaves as a short circuit. The accompanying serial NTC thermistor's resistance governs the current drawn into the sensor array, which is proportional to the temperature of the thermistor. The signal from the remaining TEDs is not accounted since the input frequency is selected such that the remaining capacitors possess too little capacitance to admit current at this frequency and so appear as open circuits. The frequency is increased such that the second highest value capacitor behaves as a short circuit as the time constant associated with the RC circuit the capacitor comprises is encountered. Any change in current is associated with the temperature of the NTC resistor in series with the second highest value capacitor. The process is performed such that the remaining temperatures of the NTC thermistors in each TED are resolved in sequence allowing the temperature profile to be determined. The unique value capacitances can be arranged in an arbitrary sequence, provided the position of the individual capacitances is known. The process therefore utilises a frequency sweep in order selectively to interrogate elements of the array.

The same effect as described above for capacitive TEDs can be achieved with a sensor array comprising TEDs that more generally comprise electronic filters (each having a unique value) which are selectively interrogated within the array. Examples of suitable electronic filters include RL filters, low-pass filters, bandpass filters and any other similar arrangements.

Instead of measuring resistance at a particular frequency to determine a temperature-dependent parameter, as described above, The temperature at a given TED can also be gauged by determining the shift between predetermined cut-off frequency (that is, the cut-off frequency at a calibration temperature) and interrogated cut-off frequency (that is, the cut-off frequency at an actual, unknown, temperature to be measured). This allows the significant temperature-dependent parameter exhibited by some capacitors to be exploitable by having TEDs comprising fixed resistors in series with temperature-dependent capacitors. Each TED comprises an RC circuit with a unique predetermined cut-off frequency. The temperature at a given TED is inferred by selectively interrogating TEDs by manipulating input frequency and determining capacitance or the shift between interrogated and predetermined cut-off frequency. A temperature profile is thereby derived by accumulating the inferred temperature across the array.

Alternatively, an inductor can be introduced into the TEDs <NUM> shown in <FIG>, thus forming an RLC circuit, which exhibits resonance. The RLC circuit of each TED <NUM> possesses a unique predetermined resonant frequency (via appropriate selection of fixed value resistors and/or NTC/PTC thermistors <NUM>). The temperature associated with a particular RLC-based TED at a particular position is determined in isolation of other TEDs by applying a frequency across the sensor terminals <NUM> which is close to the predetermined resonant frequency associated with that particular TED. By modulating the applied frequency around the predetermined resonant point for that particular TED, the true resonant frequency can be found. The shift in resonant frequency exhibits a temperature-dependence from which temperature can be deduced. By interrogating the array in this manner, the temperature profile throughout the vessel can be deduced directly. The computation of Equation <NUM> or <NUM> is achieved via numerical integration of the resulting temperature profile.

<FIG> shows a TED <NUM> configuration comprised of diodes <NUM> parallel to resistive elements <NUM> and the combination in series with further resistive elements <NUM>. Multiple TEDs <NUM> are connected in parallel to form a sensor <NUM>. The TEDs can act as shunts in the parallel arrangement. Diodes exhibit temperature-dependent phenomena with respect to forward operating, reverse breakdown and current leakage performance characteristics. The current drawn by the sensor for a fixed voltage corresponds to an aggregate of temperature-dependent parameter of the TEDs, which corresponds with the useful volume once the appropriate signal conditioning has been applied. The leakage or reverse breakdown characteristics and their dependence on temperature are exploited by the series and parallel arrangements. Forward operating performance and its dependence on temperature can be exploited by reversing the orientation of all diodes <NUM>. A sensor comprised of a serial configuration of diode-based TEDs <NUM> is equally suitable.

<FIG> shows an arrangement of grounded gate/base transistor <NUM> TEDs <NUM> connected in parallel to resistive elements <NUM>; in turn the combination is in series with further resistive elements <NUM>. The TEDs <NUM> are connected in parallel to form a sensor <NUM>. The parallel arrangement of TEDs forms a shunt circuit. There is a variety of transistor-based implementations that are conceivable including a number of bipolar and field effect approaches. Temperature-dependent phenomena associated with the intrinsic diode that exists between the collector/emitter or drain/source are exploited along with any leakage characteristics as discussed for diodes. A sensor comprised of a serial configuration of transistor-based TEDs <NUM> is equally suitable.

<FIG> shows an arrangement of biased gate/base transistor <NUM> TEDs <NUM> connected in parallel to resistive elements <NUM>, which combination is in series with further resistive elements <NUM>. Reactive elements can be used in place of the resistive elements <NUM>. The TEDs <NUM> are connected in parallel to form a sensor <NUM>. The parallel arrangement of TEDs forms a shunt circuit. In the biased transistor <NUM> instance, no more than three electrical terminals <NUM> are required to determine the useful heating or coolant fluid volume. The biasing facilitates control of the threshold temperature beyond which forward conduction takes place. The arrangements in <FIG>, <FIG> can be based around any type of semiconducting device such as field effect transistors, bipolar transistors, thyristors, etc. A sensor comprised of a serial configuration of biased-transistor-based TEDs <NUM> is equally suitable.

<FIG> shows a circuit <NUM> with a thermocline sensor <NUM> comprising an array of TEDs <NUM> (e.g. a shunt circuit with transistors or diodes - as described with reference to <FIG>) in parallel to a thermometer <NUM> (as used herein, the term "thermometer" includes any form of temperature sensor, and as such does not necessarily actually provide a measurement of temperature). The thermometer <NUM> is comprised of a thermistor <NUM> (NTC or PTC), having a resistance Rr in a serial arrangement with a capacitor <NUM>, with capacitance C. The arrangement of the circuit <NUM> thereby allows a temperature reference from the thermometer <NUM> to be determined separately to the output from the thermocline sensor <NUM>, for example by using impedance isolation. Impedance isolation is, for example, afforded by the Resistor-Capacitor (RC) construction of the thermometer <NUM> and by operating the circuit <NUM> so as to exploit the filter properties of the RC thermometer. Alternatively, impedance isolation is achievable using a thermometer with an inductor, rather than capacitor (i.e. Resistor-Inductor). <FIG> shows a combination comprising a circuit <NUM> and a controller <NUM>, wherein isolating signals from the thermocline sensor <NUM> and thermometer <NUM> is achieved by the controller and/or arrangement of the circuit <NUM> and its components.

A signal indicative of the useable volume of water in the vessel <NUM> is obtained on application of a Direct Current (DC) signal - according to the response from the thermocline sensor <NUM> - and a signal indicative of temperature at the point of the thermometer <NUM> on application of an Alternating Current (AC) signal. The thermometer <NUM> also allows the signal of the thermocline sensor <NUM> to be normalised.

In the example shown, a single thermometer <NUM> is located at a point aligned with the vessel outlet <NUM>. TEDs <NUM> are placed within the vessel <NUM> or externally to the vessel. The thermometer <NUM> provides a measure of temperature adjacent its position.

It is advantageous for the circuit <NUM>, in particular the thermocline sensor <NUM>, to be fitted to an outside thermally conductive wall of the vessel <NUM>, since this enables the circuit <NUM> to be retrofit. However, for vessels <NUM> with highly conductive walls (such as thick, e.g. ><NUM>-<NUM>, and/or British Standard grade <NUM> Copper walls) a significant discrepancy between the internal water and external wall temperatures arises due to differences in heat transfer between the water within the vessel <NUM> and the vessel wall. The discrepancy - most significant when there is a thermocline with a steep temperature gradient across it - is observed as a blurring of the otherwise sharp thermocline temperature transition point when inferring internal water temperature from the vessel wall. The accuracy to which the thermocline position is determined from measures of thermal properties of the vessel wall is therefore adversely affected. A model (referred to as a "wall model" herein) is used to obviate the thermal effects on measurements from a sensor that measures the thermal properties of fluid within the vessel through the vessel wall. The temperature profile and/or thermal exergy content of the fluid within the vessel, is available to be inferred by a sensor, such as the thermocline sensor <NUM>, on an external wall of an insulated vessel, more accurately than without accounting for the thermal effects of the vessel wall. In one example, the wall model allows a sensor to be located adjacent to a vessel wall when the vessel and sensor are assembled during original manufacturing (and not just retrofit); this allows the sensor to be fixed to the vessel and then the insulation applied over the top of the vessel and sensor. The wall model is adapted according to measurements from the thermometer <NUM>.

The wall model is based on the thermal dynamics of heat flux across the vessel wall due to a stratified body of water contained within the vessel and applying analytical and/or interpolative techniques (for example a numerical spline method) in order to obtain a solution. In one example, a wall heat flux function that maps the temperature and temperature gradient of the external wall of the vessel to an empirical or computed relationship between a position on the vessel wall and heat flux is used, and parameterisation of such a function is used on the basis of features of the vessel wall temperature and temperature gradient.

More elaborate wall models, for example accounting for transient thermal conduction, are alternatively applied, wherein the influence of fluid flow within the vessel during operation, distributed heat capacitance and conduction to the ambient environment is considered so that the sensor is capable of accounting for these effects.

Knowledge of the thermal dynamics of the vessel and fluid, allows the output of the thermocline sensor <NUM> to be fit to a thermal model of the vessel and fluid. The accuracy of measurements from the thermocline sensor <NUM> is thereby maintained with fewer array elements, e.g. TEDs <NUM>. For example, <NUM>-<NUM> array elements allows for the thermal energy of the fluid to be suitably determined using; more preferably <NUM>-<NUM> array elements are used, but no fewer than <NUM>-<NUM> array elements are used.

In an alternative example, a linear exergy sensor composed of independent individual sensors traversing strata of fluid within a vessel is used to obtain a temperature profile of the fluid. In one example, the independent array of sensors comprises at least one of: a thermistor, thermocouple and/or any of the thermocline sensors <NUM> described herein. A signal compressor is used to aggregate the outputs from the sensors in order to determine the position of the thermocline and thus the thermal exergy of the fluid. When the number of independent sensors is small, e.g. <<NUM>-<NUM> independent sensors, the output of the independent sensors is fit to a thermal model in order to improve the accuracy of the temperature profile, for example using regressions or interpolation techniques (such as spline fitting).

<FIG> shows an alternative circuit <NUM> to the example shown in <FIG>, whereby a plurality of thermometers <NUM> are connected in parallel to the thermocline sensor <NUM> so as to traverse different positions of the vessel <NUM>, for example the vessel outlet <NUM>, inlet <NUM> and/or intermediate positions therein. In one example, the thermometers <NUM> are distributed along the vessel at isochoric intervals. The low pass leg of the thermometer <NUM> arrangement is replicated in the circuit <NUM> introducing additional pole and/or zero time terms for multiple impedance isolated thermometers <NUM> in different locations of the vessel <NUM>. An array of impedance isolated thermometers <NUM> allows individual temperature readings to be made for each thermometer <NUM>. A means of compiling a temperature profile of the fluid in the vessel is also achieved by independently interrogating each thermometer <NUM> of such an array, and thereby aggregate a temperature profile of the fluid within the vessel.

The output of an array of thermometers <NUM> is improved, when the array of thermometers is coupled with a sensor with finer resolution, such as a thermocline sensor <NUM> comprising a high number of PTC based TEDs <NUM>.

The volume of useful fluid within the vessel is dependent upon both the temperature distribution throughout the tank (detected either by the thermocline sensor <NUM> or an array of thermometers <NUM>) along with the temperature of any cold water used for the purposes of mixing. Monitoring the temperature of the vessel inlet <NUM>, for example using a thermometer <NUM>, and making the assumption that this is representative of inlet temperatures feeding appliances downstream of the vessel (e.g. the cold side of a shower mixer valve), Equation <NUM> is solved for the useful volume of fluid. Tc as determined using, for example, a thermometer <NUM>, is used to correct the gain and bias terms applied to the output of the thermocline sensor <NUM>. Thermometers <NUM> located at cold inlets of the vessel allow for useful volume of water delivered to end users to be determined and thermometers <NUM> located at hot outlets allows monitoring of potentially unsanitary exposures to water.

The circuits comprising the thermocline sensors <NUM> and thermometer(s) <NUM>, as shown in <FIG> and <FIG>, are arranged such that the thermocline sensor <NUM> and thermometer(s) <NUM> have a shared output terminal <NUM>. The shared output has no more than two or three (not shown) electrical terminals that are used to obtain an output from the thermocline sensor <NUM> and thermometer(s) <NUM>.

<FIG> shows a flow diagram of the combined thermocline sensor <NUM> and thermometer <NUM> circuit under AC/DC operation <NUM>. In a first step <NUM>, a DC signal is applied across terminals <NUM>, and the output signal from the circuit <NUM> across output terminals <NUM> is monitored. The output voltage, Vout, from output terminals <NUM> is subsequently recorded and, given that Rs is known and that no current flows through the thermometer <NUM>, the resistance across the thermocline sensor <NUM>, Rt, can be computed in step <NUM>. In a following step <NUM>, an AC signal is applied across the circuit <NUM> at a frequency that is far greater than the maximum anticipated value of the inverse of the zero time constant of the circuit <NUM>. The frequency is also selected so that it is high enough to avoid temperature related effects on the frequency response of the circuit (i.e. the thermocline sensor <NUM> and thermometer <NUM> circuit) when sensing the reference temperature. The output voltage, Vout, is recorded and, on the basis of the change in magnitude response of the output voltage in step <NUM> relative to the output voltage recorded in step <NUM>, Rr is computed <NUM>. Finally, the temperature associated with the computed value of Rr is correlated with Rt so that the proximity of the thermocline within the vessel <NUM> to vessel outlet <NUM> and/or the remaining useable volume of water within the vessel <NUM> is associated with the temperature to which Rr relates <NUM>. The process of AC/DC operation <NUM> is also available to be used with circuits that have multiple thermometers <NUM>, as per circuit <NUM>. Alternatively, a DC signal is used to obtain a reading from the temperature sensor <NUM> and an AC signal to obtain a signal from the thermocline sensor <NUM>.

The thermometer <NUM> is used to calibrate the output of the thermocline sensor <NUM>, detect unsanitary exposures and, where the measurement provided by the thermometer is taken close to the vessel inlet, an indication of useful volume of fluid developed downstream of the vessel. For an array of thermometers (as shown in <FIG>) where the output of each thermometer is available to be determined independently, the array is used in addition to the thermocline sensor <NUM> to determine the useful volume of fluid within the vessel developed downstream of the vessel.

<FIG> shows signal processing of the output signal from the thermocline sensor <NUM> in the form of a flow diagram <NUM>. Once an output signal has been obtained from the thermocline sensor <NUM> in a first step <NUM>, the signal is conditioned such that the useful volume of fluid within the vessel <NUM> is accurately derivable, for example by using numerical integration of TED-detected temperature-dependent parameters; applying a gain and/or bias of the thermocline sensor <NUM>; and applying a wall model and/or model fitting <NUM>. The signal conditioned in step <NUM> is further processed in order to derive the useful volume of fluid within the vessel <NUM>, for example by using low pass filters, Savitzky-Golay filters, moving averages and local regression <NUM>. The output from step <NUM> is made available to an algorithm for logging draw events (a "log algorithm"), which logs draw events that result in the removal of fluid from the vessel <NUM>. The logged draws are displayed to the user <NUM> and/or recorded <NUM>, for example in the form of water usage history, energy consumption and/or the remaining amount of useable water within the vessel <NUM>. A predictive model is applied to the information made available to the log algorithm <NUM>. For example a Markov model is used to anticipate when heating of the water within the vessel is required and/or when the water within the vessel will surpass an unsanitary threshold, as unsanitary exposures tend to coincide with large draw events (as indicated by the rate of change of the output from a thermocline sensor <NUM>), for example during shower usage, which is of particular concern due to the added risk of inhaling contaminated water that has been aerolised.

The thermocline sensor <NUM> and controller <NUM>, having the ability to determine the position of the thermocline in a stratified body of water within a vessel (and thus determine the exergy within the vessel), provide an indication of the level of the thermocline relative to the position of the vessel outlet <NUM> (or outlets) and therefore react (e.g. by providing a sanitary hazard flag or scheduling heating of the fluid within the vessel) in anticipation of unsanitary draw events from the vessel. The addition of at least one thermometer <NUM> provides greater confidence of the temperature of fluid at a given position within the vessel, preferably at the vessel outlet <NUM> or inlet <NUM>. The reliability of determining the position of the thermocline relative to a reference position is thereby improved and the sanitary conditions of water at a given position is determinable with a greater degree of certainty. The thermometer <NUM> also provides a means of calibrating the output of the thermocline sensor <NUM> with respect to a reference temperature determined from one or more of the thermometers <NUM>. If the predictive model determines that user exposure to unsanitary water is likely, a sanitary hazard flag is raised <NUM>, either as a warning detectable by the user <NUM> or as a trigger for a response to prevent exposure to unsanitary water. The predictive algorithm also schedules heating of water if it anticipates that the volume of useful water is likely to be expended <NUM>. A determination is made at step <NUM> as to whether a heat source for heating water in the vessel is currently active - if the heat source is active, then a threshold is logged and corrected <NUM>. A disaggregate of the volume of fluid removed from the vessel and the change in sensor output is determined at step <NUM> in order to understand the user's draw activity. If a heating source is on, the threshold rate of the change in the output of the thermocline sensor associated with a draw event is corrected to recover the true recording of useful hot water drawn from the vessel. By isolating the effects of standing heat loss, and heating of the fluid due to a heating element, a more accurate indication of removal of fluid is provided. A schedule of activity of the heating element is used in addition to outputs from the controller operating the thermal source to aid decoupling of heating and draw events. Subsequently, a determination as to the rate of change of the available quantity of hot water below a threshold rate <NUM> is made. Otherwise, an uncorrected log threshold is used as a parameter for step <NUM>. If the rate of change of the useful quantity of hot water is not below the threshold rate, the process <NUM> loops; if not, logging of the useful quantity of hot water, energy usage and/or thermocline position begins <NUM> and continues according to a determination of the rate of change of the available quantity of water at a useful temperature in step <NUM> until this rate falls below the threshold, at which point logging of useful volume of fluid, energy usage and/or thermocline position ends <NUM>. Steps <NUM>-<NUM> are used to identify draw events on the basis of the changing output of a thermocline sensor or temperature array whose output is aggregated into a single measurement of useful volume of water within the vessel <NUM>. Identification of draw events is exploited to record information on historic fluid usage, for example with an aim to inform users of their consumption habits; prime a state transition matrix within a Markov chain to predict the timing and size of future draw events for the purposes of scheduling heat sources and flag potentially unsanitary episodes or likely future instances where the outlet temperature may drop beneath a sterilising threshold for a pathogen, such as Legionella. Additionally, an algorithmic procedure is provided to condition the output of the thermocline sensor <NUM> and track the changes in state within the vessel which occur due to draw events during operation. Steps <NUM>-<NUM> are linked the log usage display step <NUM>, so that the log usage can be presented or indicated to the user.

The controller <NUM> and/or processor <NUM> is able to identify distinct modes of heat loss from the vessel. Draw events from the changing output of the thermocline sensor <NUM> with time are identified by sudden changes detected by the thermocline sensor <NUM>, rather than when the output of the thermocline sensor drops gradually as a result of standing heat losses.

Many domestic hot water systems have an internal heat exchanger through which hot water is extracted. In this example, knowledge of the thermocline position alone is insufficient to resolve the quantity of useable hot water in the vessel. In such cases, the temperature at the top of the vessel remains substantially constant during operation and the temperature of the outlet of the heat exchanger drops due to starvation as the thermocline transitions across the extent of the heat exchanger. A function that maps the water temperature gradient within the vessel to the availability of energy from a heat exchanger immersed within the vessel is provided. For example, for a helical coil, a mapping between the coil's height relative to the vertical position in the vessel, coil diameter and pitch are considered. An algorithm which maps the temperature profile within the vessel to the likely output from a heat exchanger for a given flow rate and inlet temperature is provided. Similarly, an algorithm used in combination with a thermal heat exchanger model and a one-dimensional or two-dimensional vessel stratification model in order to resolve the rate of change in outlet temperature for a given flow rate and inlet temperature is used, which then computes useable energy, mass or volume of hot water for a given useful temperature reference value. By providing a model of the heat exchanger the output of the thermocline sensor is available to account for the influence of the heat exchanger and more therefore allow for a more accurate determination of the useful volume of fluid.

<FIG> shows a schematic diagram of a device, for example in the form of a processor <NUM>, for identifying removal of fluid from the vessel <NUM> - a draw event. An input indicative of thermal properties of fluid within the vessel is received by the processor <NUM> from a sensor <NUM>, for example the thermocline sensor <NUM>. The processor identifies a draw event by considering the rate of change of the output from the sensor <NUM> in a first processing step <NUM>. A determination is made by the processor as to whether the change in output signal is due to removal of fluid from the vessel or due to static heat loss from the vessel <NUM>; if the determination indicates the former cause, the processor outputs an instruction to induce dispatch of energy to a heat source to manipulate the temperature of the fluid within the vessel <NUM>.

<FIG> shows a schematic diagram of a device, for example in the form of a processor <NUM>, which receives an output from a sensor <NUM> that determines thermal properties of a fluid within the vessel through a conductive barrier, such as the vessel wall <NUM>. The processor applies a corrective function to the signal received from the sensor <NUM> in order to account for the thermal effects of the vessel wall and indicate more accurately the thermal properties of the fluid within the vessel <NUM>. The useful volume of fluid within the vessel is therefore determined <NUM> more accurately using a sensor that measures thermal properties of the fluid through a conductive barrier by using the adjusted measure of the thermal properties of the fluid by the processor <NUM>. The vessel <NUM> and sensor <NUM> are shown enveloped by a layer of thermal insulation <NUM>.

The vessel <NUM> described with reference to <FIG> is for example an immersion heating tank or a similar installation, with an inlet <NUM> and an outlet <NUM> in fluid communication with the vessel content. The vessel can take other forms, for example a heat exchange vessel or a heat store vessel where a fluid conduit (with an inlet and outlet) is in thermal communication, but not fluid communication, with the vessel content; or a vessel such as a kettle where the fluid inlet and outlet are combined in a single aperture. Common to the vessels is a fluid with a temperature profile extending between a first region and a second region of the vessel, typically due to a localised thermal source or drain, and/or thermal stratification in the vessel.

In one example, the thermocline sensor <NUM> is integrated onto a flexible strip, such as a strip of composite copper, polymer composite (e.g. Espanex or Kapton) and any of the aforementioned circuitry is available to be printed onto the flexible strip surface prior to etching in a ferric chloride bath. For easy retrofit of the thermocline sensor, a portion of the outer insulation of the vessel <NUM>, as is commonly present, is removed and the sensor located in the recess formed from the removal of the insulation. The circuitry comprising the thermocline sensor <NUM> is arranged such that an adhesive layer is appended to the vessel <NUM> wall surface, thereby allowing a layer of flexible polymer above the adhesive layer to be in thermal contact with the vessel wall. Above the flexible polymer layer, a layer of copper and/or printed circuit board trace is present with a layer of electrical components is provided above therein. An outer insulation layer on the thermocline sensor arrangement is placed as a final layer. It is therefore envisaged that thermocline sensors <NUM> composed on reels of flexible strips of adhesive tape are manufactured by a continuous method of production. A kit of parts for easy retrofit onto a vessel is therefore available.

In one example the PTC or NTC elements used in the thermocline sensor <NUM> have a non-linear response (e.g. as per a thermistor made of Barium Titanate), in particular around the Curie transition temperature. The Curie transition temperature is used to provide an integral limit that differentiates between useful and non-useful energy. Advantageously the response of a PTC resistor will occur only above a certain threshold thereby introducing an inherent threshold for judging a useful temperature.

It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.

Claim 1:
A sensor (<NUM>) for measuring a temperature profile of a fluid within a vessel (<NUM>), the vessel (<NUM>) having a first region and a second region and the fluid having a temperature profile extending between the first region and the second region,
the sensor (<NUM>) comprising an array of elements (<NUM>), each element (<NUM>) having a temperature-dependent parameter, the array being capable of deployment within or adjacent the vessel (<NUM>) such that the array extends along the vessel (<NUM>) for measuring the temperature profile,
characterised in that the elements (<NUM>) of the array are coupled together between an input and an output, the input being coupled or capable of being coupled to a driving source for driving the sensor, and the output being coupled or capable of being coupled to a detector for measuring an aggregate of the temperature-dependent parameter from the array of elements (<NUM>),
wherein the array comprises a substrate that can be cut to length to determine the number of elements (<NUM>) within the array.