Heating system

Abstract

A heating system comprises a vessel for containing a fluid for receiving or delivering heat, a heat pump arranged to provide heat to fluid of the vessel, an array of temperature sensors arranged to sense temperatures at different heights of the vessel, and a controller configured to determine a thermal energy in the vessel in dependence on inputs from the array of temperature sensors, determine a transient response in the vessel in dependence on inputs from the array of temperature sensors, determine a predicted heat demand, and control operation of the heat pump in dependence on the thermal energy in the vessel, the transient response in the vessel and the predicted heat demand. The heating system is therefore arranged to increase the efficiency of heat transfer from a heating device to a user device. Also described are a method and a controller for a heating system.

Description

[0001] Heating System

[0002] The present disclosure relates to a thermal storage vessel for containing a heat store fluid for receiving or delivering heat.

[0003] Efficiently transferring heat in domestic heat stores is important, particularly as there is a current trend to move away from fossil fuel powered heaters to electrical and solar heating devices. These devices typically operate at lower power than fossil fuel burners and boilers, meaning that there is a greater need for efficient heat transfer from the heating device to the end use (e.g. space heating or hot water).

[0004] Furthermore, as heat stores become more complicated to increase their heat transfer efficiency, there is a need to simplify the servicing procedure for the heat stores. T raditional heat stores may be sealed devices, meaning that an internal failure of a subsystems can result in the heat stores rendered unusable. Being able to easily remove the fluid from the heat stores would allow for servicing of subsystems to become a more routine operation, increasing the lifetime of the heat stores.

[0005] The present disclosure aims to alleviate these and other problems.

[0006] According to a first aspect of the disclosure there is provided a heating system comprising a thermal storage vessel for containing a heat store fluid for receiving or delivering heat, a heating element arranged in an upper portion of the thermal storage vessel for immersion in the heat store fluid; a conduit with a pump arranged to draw heat store fluid from a lower portion of the thermal storage vessel and provide it to an upper portion of the thermal storage vessel; and a coil heat exchanger arranged for immersion in the heat store fluid and extending substantially along the height of the thermal storage vessel.

[0007] Advantageously, the coil heat exchanger extending substantially along the height of the vessel may improve the efficiency of the heating system. The pump and heating element may work in tandem to provide quick heat inputs to the vessel when a sudden heat demand is required.

[0008] The coiled section of the coil heat exchanger may extend substantially along the height of the vessel. The surface area of the coil heat exchanger may therefore be distributed substantially evenly along the height of the vessel.

[0009] The coil heat exchanger may be a coiled pipe. Advantageously this may be a cost-effective means of transferring heat between two fluids.

[0010] At least a portion of the outer surface of the coil heat exchanger may include formations arranged to increase the surface area of the coil heat exchanger. This may increase the rate of heat transfer between the fluid in the vessel and fluid flowing through the coil. The formations may be corrugations or fins. These may be a cost-effective means of increasing the surface area of the coil heat exchanger. The formations may be included only in an upper portion of the coil heat exchanger.

[0011] The pump may be a submersible pump arranged inside the thermal storage vessel. The heating element may be an electric heating element.

[0012] The heating system may further comprise a diffuser arranged at an outlet of the conduit and configured to reduce a velocity of heat store fluid provided to the upper portion of the thermal storage vessel. This may reduce the amount of mixing within the vessel when operating in a top up mode.

[0013] The heating system may further comprise a baffle arranged at an intermediate height in the thermal storage vessel. Advantageously, the baffle may improve the separation of a warm and cold region within the vessel to improve the efficiency of sudden heat inputs to the vessel.

[0014] Preferably the coil heat exchanger is arranged to receive heat from the thermal storage vessel. The coil heat exchanger may be arranged to provide heat to potable water and / or a space heating system. An inlet to the coil heat exchanger may be arranged at a lower portion of the thermal storage vessel and an outlet from the coil heat exchanger may be arranged at an upper portion of the thermal storage vessel.

[0015] The heating system may further comprise a second coil heat exchanger arranged within the thermal storage vessel. This may increase the versatility of the heating system by allowing for additional heat inputs or outputs from the vessel.

[0016] The second coil heat exchanger may be arranged in an upper portion of the thermal storage vessel. This may increase the rate of heat transfer from / to the fluid in the second heat exchanger. At least a portion of the outer surface of the second coil heat exchanger may include formations arranged to increase the surface area of the second coil heat exchanger. The formations may be corrugations and / or fins. The second coil heat exchanger may be arranged to receive heat from the thermal storage vessel. The second coil heat exchanger may be arranged to provide heat to potable water and / or a space heating system. An inlet to the second coil heat exchanger may be arranged at a middle portion of the thermal storage vessel and an outlet from the second coil heat exchanger may be arranged at an upper portion of the thermal storage vessel. The second coil heat exchanger may be arranged to provide heat to the thermal storage vessel. The second coil heat exchanger may be arranged to provide heat from a heat pump system. An inlet to the second coil heat exchanger may be arranged at an upper portion of the thermal storage vessel and an outlet from the second coil heat exchanger may be arranged at a middle portion of the thermal storage vessel.

[0017] The heating system may further comprise a plurality a temperature sensors configured to determine a quantity of heat stored in the thermal storage vessel and / or a distribution of heat stored within the thermal storage vessel. These may improve the efficiency of the heating system as they can provide information on the quantity of heat stored in the vessel.

[0018] The conduit may be configurable into a drain configuration for expelling heat store fluid out of the thermal storage vessel. Advantageously, this may make servicing or attending to faults developed within the heating system easier as the thermal storage vessel can be easily drained.

[0019] According to another aspect of the disclosure there is provided a heating system comprising: a thermal storage vessel for containing a heat store fluid for receiving or delivering heat; a heat source arranged in an upper portion of the thermal storage vessel to provide heat to the heat store fluid; and a conduit with a pump arranged to draw heat store fluid from a lower portion of the thermal storage vessel and provide it to the heat source or an upper portion of the thermal storage vessel; wherein the conduit is configurable into a drain configuration for expelling heat store fluid out of the thermal storage vessel.

[0020] This may make servicing or attending to faults developed within the heating system easier as the thermal storage vessel can be easily drained.

[0021] The heating system may be as aforementioned.

[0022] The conduit may comprise a junction with a first branch arranged to provide heat store fluid to an upper portion of the thermal storage vessel and a second branch arranged to expel heat store fluid out of the thermal storage vessel. The heating system may further comprise a three-port valve at the junction for selection of the first branch or the second branch. This may provide a convenient means to direct the flow path of fluid in the conduit. The three- port valve may be an electronically controlled three- port valve. This may allow for easy draining of the thermal storage vessel and may allow for the inclusion of safety interlocks to allow the vessel to be drained under suitable conditions.

[0023] The heating system may further comprise a controller configured to control the electrical components of the heating system, such as the pump, the heating source, and / or the three-port valve. This may improve the efficiency and use of the heating system.

[0024] The conduit may be deformable and configured to extend outside the thermal storage vessel in the drain configuration. The conduit may comprise a flexible portion.

[0025] The conduit may comprise an outlet port with a coupling configured to mate with a conduit extension.

[0026] The pump is preferably a submersible pump arranged inside the thermal storage vessel.

[0027] The heat source may be a heating element. The heat source may be an electric heating element. The conduit may be arranged to provide heat store fluid to an upper portion of the thermal storage vessel. The heating system may further comprise a diffuser coupled to an outlet of the conduit. The diffuser can serve to reduce a velocity of heat store fluid provided to the upper portion of the thermal storage vessel. The heating system may further comprise a baffle arranged at an intermediate height in the thermal storage vessel. The heating system may further comprise a plurality of temperature sensors configured to determine a quantity of heat stored in the thermal storage vessel and / or a distribution of heat stored within the thermal storage vessel.

[0028] The heat source may be a heat exchanger. The conduit may be arranged to provide heat store fluid to the heat exchanger The heat source may be a coil heat exchanger. The heat source may be a plate heat exchanger. The heat source may be a heat exchanger with two forced flows.

[0029] The heating system may further comprise a heat exchanger or a further heat exchanger arranged to receive heat from heat store fluid. The heat exchanger or further heat exchanger may be arranged inside the thermal storage vessel. The heat exchanger or further heat exchanger may be arranged outside the thermal storage vessel. The heat exchanger or further heat exchanger may be arranged to provide heat to potable water and / or a space heating system. The heat exchanger or further heat exchanger may be a coil heat exchanger. The heat exchanger or further heat exchanger may be a plate heat exchanger. The heat exchanger or further heat exchanger may be a heat exchanger with two forced flows.

[0030] According to another aspect of the disclosure there is provided a heating system comprising: a vessel for containing a fluid for receiving or delivering heat; a heat pump arranged to provide heat to fluid of the vessel; one or more temperature sensors, preferably an array of temperature sensors arranged to sense temperatures at different heights of the vessel; and a controller configured to: determine a thermal energy in the vessel in dependence on inputs from the one or more temperature sensors; determine a transient response in the vessel in dependence on inputs from the one or more temperature sensors; determine a predicted heat demand; and control operation of the heat pump in dependence on the thermal energy in the vessel, the transient response in the vessel and the predicted heat demand. The heating system or features of the heating system may be as aforementioned.

[0031] The controller can enable a balance between provision of a predicted heat demand just in time at the best available coefficient of performance and avoidance of unnecessary or excessive on-off cycling of the heat pump.

[0032] The controller may be configured to monitor the thermal energy in the vessel and the transient response in the vessel. The transient response may be continuously or periodically monitored. The controller may be configured to calculate a thermal energy in the vessel from measurements from the one or more temperature sensors. The controller may be configured to identify a transient response in the vessel from measurements from the one or more temperature sensors. The controller may be configured to characterise a transient response in the vessel from measurements from the one or more temperature sensors. A transient response may be a time-resolved change in thermal energy in the vessel.

[0033] The transient response may be in response to operation of the heat pump. The transient response may be a time delay between switching the heat pump on and steady state provision of heat to the vessel. The transient response may also refer to the change in temperature of fluid stored in the vessel over time, for instance an oscillation of fluid temperature in the vessel about a desired fluid temperature. This oscillation may occur due to a switching on and off of the heat pump to maintain the desired temperature. The controller may be configured to control the heat pump in dependence on the known oscillatory characteristics of the vessel. The transient response may also refer to a derivative of the temperature change in the vessel with respect to time, or a rate of change of temperature in the vessel. The transient response may be a response to a change of conditions until a steady system state is established. The controller may be configured to determine occurrence of operation of the heat pump. The controller may be configured to determine a time delay between switching the heat pump on and steady state provision of heat to the vessel based on inputs from the one or more temperature sensors. The controller may be configured to control operation of the heat pump to meet the predicted heat demand in dependence on the time delay. The transient response may be in response to occurrence of an event drawing heat from the vessel (e.g. drawing of hot water or a space heating demand). The transient response may be a decrease of thermal energy in the vessel in response to an event drawing heat from the vessel (e.g. drawing of hot water or a space heating demand). The transient response may be an increase of thermal energy in the vessel in response to conclusion of an event drawing heat from the vessel (e.g. drawing of hot water or a space heating demand). The controller may be configured to determine occurrence of an event drawing heat from the vessel (e.g. drawing of hot water or a space heating demand).

[0034] The controller may be configured to determine a rate of change of the thermal energy. The controller may be configured to control operation of the heat pump in dependence on the rate of change of the thermal energy. The heating system may further comprise a further heat source. The further heat source may be one or more electric heating elements optionally for immersion in the fluid. The controller may be configured to control operation of the further heat source in dependence on the rate of change of the thermal energy. The controller may be configured to cause the further heat source to switch on when the rate of change of the thermal energy exceeds a threshold.

[0035] The thermal energy in the vessel may be a thermal energy above a threshold temperature. The vessel may be a hot water tank or a heat store. The heating system may comprise a heat exchanger for receiving heat from the heat pump. The heat exchanger may be arranged inside the vessel or outside the vessel. The heating system may comprise a heat exchanger for providing heat to a flow of fluid. The heat exchanger may be arranged inside the vessel or outside the vessel. The heat exchanger may be a coil heat exchanger. The heat exchanger may be a plate heat exchanger. The heating system may comprise one or more temperature and / or flow sensors in one or more conduits to or from the vessel.

[0036] According to another aspect of the disclosure there is provided a heating system comprising: a vessel for containing a fluid for receiving or delivering heat; a heat pump arranged to provide heat to fluid of the vessel; an electric heating element arranged in the vessel for immersion in the fluid; one or more temperature sensors, preferably an array of temperature sensors arranged to sense temperatures at different heights of the vessel; and a controller configured to: determine a thermal energy in the vessel and a rate of change of the thermal energy in dependence on inputs from the one or more temperature sensors; determine a predicted heat demand; control operation of the heat pump in dependence on the thermal energy in the vessel and the predicted heat demand; and control the electric heating element to switch on when the rate of change of the thermal energy exceeds a threshold. The heating system or features of the heating system may be as aforementioned.

[0037] The controller can enable provision of a predicted heat demand just in time at the best available coefficient of performance.

[0038] The controller may be configured to monitor the thermal energy in the vessel and the rate of change of the thermal energy. The controller may continuously or periodically monitor the thermal energy in the vessel and / or the rate of change of the thermal energy.

[0039] The controller may be configured to determine a transient response in the vessel in response to operation of the heat pump; and control operation of the heat pump in dependence on the transient response. The controller may be configured to determine a time delay between switching the heat pump on and steady state provision of heat to the vessel; and to control operation of the heat pump to meet the predicted heat demand in dependence on the time delay. The controller may be configured to determine a minimum required thermal energy in the vessel and control the electric heating element and / or heat pump to switch on when the thermal energy falls below the minimum required thermal energy.

[0040] According to another aspect of the disclosure there is provided a controller for a heating system with a vessel for containing a fluid for receiving or delivering heat; a heat pump arranged to provide heat to fluid of the vessel; one or more temperature sensors, preferably an array of temperature sensors arranged to sense temperatures at different heights of the vessel; wherein the controller is configured to: determine a thermal energy in the vessel in dependence on inputs from the one or more temperature sensors; determine a transient response in the vessel in dependence on inputs from the one or more temperature sensors; determine a predicted heat demand; and control operation of the heat pump in dependence on the thermal energy in the vessel, the transient response in the vessel and the predicted heat demand. The controller or features of the controller may be as aforementioned.

[0041] According to another aspect of the disclosure there is provided a method of controlling a heating system with a vessel for containing a fluid for receiving or delivering heat; a heat pump arranged to provide heat to fluid of the vessel; one or more temperature sensors, preferably an array of temperature sensors arranged to sense temperatures at different heights of the vessel; wherein the controller is configured to: determine a thermal energy in the vessel in dependence on inputs from the one or more temperature sensors; determine a transient response in the vessel in dependence on inputs from the one or more temperature sensors; determine a predicted heat demand; and control operation of the heat pump in dependence on the thermal energy in the vessel, the transient response in the vessel and the predicted heat demand. The method may include steps as executed by a controller as aforementioned.

[0042] According to another aspect of the disclosure there is provided a heating system comprising: a vessel for containing a heat store fluid for receiving or delivering heat; a heat pump arranged to provide heat to heat store fluid of the vessel; optionally an array of temperature sensors arranged to sense temperatures at different heights of the vessel; a plate heat exchanger for providing heat from the heat store fluid of the vessel to a flow of fluid; a pump configured to pump heat store fluid from the vessel to the plate heat exchanger and back to the vessel; and a controller configured to: optionally determine a thermal energy in the vessel in dependence on inputs from the array of temperature sensors; determine a heat demand at the plate heat exchanger; and control operation of the pump in dependence on the heat demand at the plate heat exchanger and optionally the thermal energy in the vessel. The heat demand at the heat exchanger may be determined by determining occurrence of a flow in a heat-receiving side of the heat exchanger. The pump may be operated to maintain a minimum, maximum, or mean temperature in the plate heat exchanger or in the fluid entering or exiting one side of the plate heat exchanger. The heat demand at the heat exchanger may be determined by determining a temperature in a heat-receiving side of the heat exchanger.

[0043] The heat demand may also be determined based on the side of the plate heat exchanger providing heat from the plate heat exchanger to a flow of fluid. The determined heat demand may be determined based on the difference in temperature of the fluid flowing into and out from the plate heat exchanger.

[0044] Controlling operation of the pump in dependence on the heat demand at the plate heat exchanger can enable particularly efficient use of heat stored in the vessel and provision of a greater quantity of hot water and higher volumetric efficiency.

[0045] The heating system or features of the heating system may be as aforementioned.

[0046] The heating system may comprise an array of temperature sensors arranged to sense temperatures at different heights of the vessel. The controller may be configured to determine a thermal energy in the vessel in dependence on inputs from the array of temperature sensors. The controller may be configured to control operation of the pump in dependence on the thermal energy in the vessel.

[0047] The pump may be a variable speed pump. The controller may be configured to control a pump rate of the pump in dependence on the heat demand at the plate heat exchanger. The controller may be configured to control a pump rate of the pump in dependence on the thermal energy in the vessel. The controller may be configured to determine a desired outlet temperature of the flow of fluid. The controller may be configured to control the pump rate of the pump at a minimum pump rate for maintaining the desired outlet temperature of the flow of fluid.

[0048] The heating system may comprise a temperature sensor for sensing an outlet temperature of the flow of fluid. The controller may be configured to control the pump rate of the pump in dependence on the outlet temperature. The controller may be configured to control the pump rate of the pump to minimise a difference between the sensed outlet temperature and the desired outlet temperature.

[0049] The heating system may comprise a flow sensor for sensing a flow of fluid at the plate heat exchanger. The controller may be configured to switch the pump on when a flow of fluid at the plate heat exchanger is sensed. The controller may be configured to control operation of the pump in dependence on a flow rate sensed at the flow sensor. The controller may be configured to control a pump rate of the pump in dependence on a flow rate sensed at the flow sensor.

[0050] The controller may be configured to control operation of the pump to minimise a temperature of heat store fluid returning from the plate heat exchanger back to the vessel.

[0051] The heating system may comprise a further heat source. The further heat source may be an electric heating element. The controller may be configured to control operation of the further heat source, optionally in dependence on the thermal energy in the vessel.

[0052] The plate heat exchanger may be arranged inside the vessel or outside the vessel. The heating system may comprise a further heat exchanger, optionally a second plate heat exchanger or a coil heat exchanger.

[0053] The flow of fluid may be a flow of heat transfer fluid or a flow of potable water. The plate heat exchanger may be arranged to provide heat to potable water and / or a space heating system. The vessel may be a hot water tank or a heat store.

[0054] According to another aspect of the disclosure there is provided a controller for a heating system with a vessel for containing a fluid for receiving or delivering heat, a heat pump arranged to provide heat to fluid of the vessel; a plate heat exchanger for providing heat from the heat store fluid of the vessel to a flow of fluid; and a pump configured to pump heat store fluid from the vessel to the plate heat exchanger and back to the vessel; wherein the controller is configured to determine a heat demand at the plate heat exchanger and control operation of the pump in dependence on the heat demand at the plate heat exchanger.

[0055] The heating system or features of the heating system may be as aforementioned.

[0056] The pump may be a variable speed pump. The controller may be configured to control a pump rate of the pump in dependence on the heat demand at the plate heat exchanger. The controller may be configured to determine a desired outlet temperature of the flow of fluid. The controller may be configured to control the pump rate of the pump at a minimum pump rate for maintaining the desired outlet temperature of the flow of fluid.

[0057] The heating system may comprise a temperature sensor for sensing an outlet temperature of the flow of fluid. The controller may be configured to control the pump rate of the pump in dependence on the outlet temperature. The controller may be configured to control the pump rate of the pump to minimise a difference between the sensed outlet temperature and the desired outlet temperature.

[0058] The heating system may comprise a flow sensor for sensing a flow of fluid at the plate heat exchanger. The controller may be configured to switch the pump on when a flow of fluid at the plate heat exchanger is sensed. The controller may be configured to control operation of the pump in dependence on a flow rate sensed at the flow sensor. The controller may be configured to control a pump rate of the pump in dependence on a flow rate sensed at the flow sensor.

[0059] The controller may be configured to control operation of the pump to minimise a temperature of heat store fluid returning from the plate heat exchanger back to the vessel.

[0060] According to another aspect of the disclosure there is provided a method of controlling a heating system with a vessel for containing a fluid for receiving or delivering heat, a heat pump arranged to provide heat to fluid of the vessel; a plate heat exchanger for providing heat from the heat store fluid of the vessel to a flow of fluid; and a pump configured to pump heat store fluid from the vessel to the plate heat exchanger and back to the vessel; wherein the method comprises determining a heat demand at the plate heat exchanger and controlling operation of the pump in dependence on the heat demand at the plate heat exchanger.

[0061] The heating system or features of the heating system may be as aforementioned.

[0062] The pump may be a variable speed pump. The method may comprise controlling a pump rate of the pump in dependence on the heat demand at the plate heat exchanger. The method may comprise determining a desired outlet temperature of the flow of fluid. The method may comprise controlling the pump rate of the pump at a minimum pump rate for maintaining the desired outlet temperature of the flow of fluid.

[0063] The heating system may comprise a temperature sensor for sensing an outlet temperature of the flow of fluid. The method may comprise controlling the pump rate of the pump in dependence on the outlet temperature. The method may comprise controlling the pump rate of the pump to minimise a difference between the sensed outlet temperature and the desired outlet temperature.

[0064] The heating system may comprise a flow sensor for sensing a flow of fluid at the plate heat exchanger. The method may comprise switching the pump on when a flow of fluid at the plate heat exchanger is sensed. The method may comprise controlling operation of the pump in dependence on a flow rate sensed at the flow sensor. The method may comprise controlling a pump rate of the pump in dependence on a flow rate sensed at the flow sensor.

[0065] The method may comprise controlling operation of the pump to minimise a temperature of heat store fluid returning from the plate heat exchanger back to the vessel.

[0066] According to another aspect of the disclosure there is provided a buffer system arrangement with intelligent control through the use of a thermocline sensor wherein a plate heat exchanger is used to draw off hot water. An outlet temperature sensor may be used to allow for the plate heat exchanger pump to be modulated to achieve a desired outlet temperature in real time. The control scheme may seek to minimise a return temperature back to the buffer by dispatching hot water at a minimum allowable temperature threshold irrespective of the demand flow rate by modulating the pump flow rate to the plate. This can enable a high degree of thermal stratification at all times and therefore maximise volumetric efficiency. The system may include: one or more inline flow meters; one or more inline electric heating elements; one or more electric heating elements for immersion in the vessel; and / or one or more diffusers at or around ports to the vessel. Inline electric heating elements can enable provision of additional heat without creating a safety risk. Diffusers can promote thermal stratification during operation.

[0067] According to another aspect of the disclosure there is provided a buffer vessel within a heat-pump system wherein there is an added heat exchanger for the provision of hot water alongside a measurement capability to determine the state of charge of the buffer alongside the time response characteristics of the heat-pump. The system may include an electric heating element for immersion in the vessel. The system may include a thermocline sensor. A controller of the system may determine rates of change of demand so as to determine power level required from heat-pump and whether or not the heat-pump and immersion are both required. A controller of the system may infer a heat-pump transient response (optionally from thermocline sensor and or heat-metering / sensors on pipework) to factor in the time delay associated with the heat-pump turning on.

[0068] Any apparatus feature as described herein may also be provided as a method feature, and vice versa.

[0069] Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, any, some and / or all features in one aspect can be applied to any, some and / or all features in any other aspect, in any appropriate combination.

[0070] It should also be appreciated that particular combinations of the various features described and defined in any aspects of the invention can be implemented and / or supplied and / or used independently.

[0071] As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure, such as a suitably programmed processor and associated memory.

[0072] As used herein, the term ‘vented’ preferably refers to a vessel that is not designed to operate containing a pressurised fluid, and the term ‘unvented’ preferably refers to a vessel that is designed to operate containing a pressurised fluid.

[0073] As used herein, the term ‘thermal storage vessel’ preferably refers to a vessel for storing thermal energy by heating fluid contained in the vessel. The fluid is preferably water. The fluid is preferably not pressurised.

[0074] As used herein, the term ‘thermal store’ is also used to refer to a thermal storage vessel.

[0075] As used herein, the term ‘an upper part’ of a vessel preferably refers to an upper half, an upper third, an upper quarter, an upper fifth or an upper tenth of the vessel (by volume or by height), with the vessel in such orientation as it is intended to be installed for use.

[0076] As used herein the terms ‘heat’ and ‘thermal energy’ are interchangeable.

[0077] 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:

[0078] Figure 1 shows a schematic of a thermal storage vessel;

[0079] Figure 2 shows a view of a sectioned thermal storage vessel; Figure 3 shows a schematic of a variant of a thermal storage vessel;

[0080] Figure 4 shows a schematic of another thermal storage vessel;

[0081] Figure 5A shows a schematic of a heating system;

[0082] Figure 5B shows a schematic of another heating system;

[0083] Figures 6A and 6B show a schematic of a thermal storage vessel and an associated temperature profile;

[0084] Figure 6C shows temperature measurements at different heights in a thermal storage vessel;

[0085] Figure 7 shows a schematic of a control scheme;

[0086] Figure 8 shows a schematic of vessel state over time;

[0087] Figure 9 shows a schematic of another heating system;

[0088] Figure 10 shows a schematic of another heating system;

[0089] Figure 11 shows a schematic of another heating system; and

[0090] Figure 12 shows two graphs comparing performances of different heating systems.

[0091] Figure 1 shows a heating system 100 comprising a thermal storage vessel 2 configured to contain fluid in the vessel 2. The vessel is formed of a body and lid 8, the lid being removable attachable to the body. The lid 2 forms a seal with the body 4 to contain fluid in the vessel 1 . A wide variety of means for removably attaching the lid to the body can be used, and generally permit detachment and re-attachment without substantial damage to the body or the lid.

[0092] The thermal storage vessel 2 serves to transfer thermal energy into and out of the heat store fluid contained by the vessel. Potable water and / or central heating fluid is isolated from the fluid inside the thermal storage vessel. The vessel is vented, as the heat store fluid need not be pressurised.

[0093] The vessel 2 features input 4 and output 6 ports for adding or removing fluid to / from the vessel 2.

[0094] A top up sub-system comprises a submersible pump 10 located in the vessel 2, in the illustrated example at the base of the vessel 2. The inlet of the submersible pump 10 draws fluid from the bottom of the vessel 2. If the submersible pump 10 is at a distance from the base of the vessel 2 then a draw conduit to the bottom of the vessel 2 can ensure that fluid is drawn from the bottom of the vessel 2. The outlet of the submersible pump 10 is coupled to an outlet conduit 12 which takes fluid from the submersible pump 10 and transfers it to the top of the vessel 2.

[0095] The submersible pump 10 is an electrically powered pump that draws fluid from the vessel 2 that surrounds the submersible pump 10. The submersible pump 10 is controlled by a controller (not shown) that can vary the speed of the submersible pump 10, varying the flow rate of the fluid from the pump. The submersible pump 10 is conveniently arranged near the base of the vessel 2 to permit operation in a cooler portion of the vessel.

[0096] A diffuser 14 is arranged at the end of the outlet conduit 12 from the submersible pump 10, where the heat store fluid is returned from the outlet conduit 12 back to the body of heat store fluid in the vessel. The diffuser 14 is configured to reduce the velocity of the fluid leaving the diffuser 14, such that the fluid is diffused gently back into the vessel 2 so as to reduce excessive mixing of the fluid which would affect the thermal stratification of the heat store fluid in the vessel. In the illustration, the diffuser 14 is provided in an upper part of the vessel.

[0097] The diffuser 14 is arranged to discharge heat store fluid in proximity to an electric heating element 30 (also referred to e.g. as an immersion element) in an upper part of the vessel. The diffuser 14 spreads out the fluid from the conduit 12 at a low velocity, reducing the amount of mixing of the fluid in the vessel 2. By switching on the electric heating element 30 and the third submersible pump 14, an on-demand portion of heat can be provided to the vessel 2 and thus to a user (e.g. to satisfy an immediate hot water demand, or an immediate space heating demand). This can enable on-demand topping up of heating availability quickly and without relying on an external source, such as a heat pump, a solar panel or a boiler, which may not be able to provide heat immediately. In an example the electric heating element 30 is a direct electric immersion heater. In a variant the electric heating element 30 is replaced by a different type of heating element that can provide immediate heat, for instance from a heating element associated with a gas burner.

[0098] An array of temperature sensors 20 is arranged to sense temperatures at different heights in the vessel. The array of temperature sensors 20 (also referred to as a thermocline sensor) can permit detection of the state of thermal stratification of heat store fluid in the vessel, which can give an indication of the heat available for use from the thermal store, depending on the thermal profile.

[0099] A baffle 40 may be provided to further improve stratification within the vessel 2 and help maintain a cooler region in the bottom of the vessel 2. The baffle 40 is preferably located halfway between the bottom and the top of the vessel 2. The baffle 40 is usefully provided below heat input into the thermal storage vessel 2 to promote stratification, in the illustrated example below the electric heating element 30. The baffle 40 can reduce convection and heat transfer from the heat store fluid surrounding the electric heating element 30 to the fluid in the cooler region at the base of the vessel 2. The baffle 40 is preferably made from a thermally insulating material.

[0100] A heat exchanger coil 50 is disposed within the vessel 2. The coil 50 is a coiled hollow tube to allow fluid to flow within the coil 50. The coil 50 is preferably formed from a material with a high thermal conductivity coefficient, for instance copper, brass, or stainless steel.

[0101] To maximise the surface area of the coil, the outer surface of the coil 50 is preferably corrugated and / or includes fins or other structures to increase the surface area or heat transfer area of the coil 50. Increasing the surface area of the coil 50 increases the rate of heat transfer for a given temperature difference between the fluid surrounding the coil 50 and the fluid within the coil 50. The corrugations, fins or other surface-increasing structures may be included in the entire length of the coil. In a variant the corrugations, fins or other surface-increasing structures may be included only in a portion of the coil. For instance the corrugations, fins or other surface-increasing structures may be included in an upper portion of the coil, where in some situations more heat may be available than in an upper portion of the coil 50, and rapid heat transfer in the upper portion of the coil 50 may be especially important in order to achieve a desired temperature in fluid passing through the coil 50.

[0102] The coil 50 is disposed substantially along the height of the vessel 2, maximising the total surface area of the coil 50 within the vessel 2. The coil 50 may be formed from a corrugated material, thereby further increasing the surface area of the coil 50 exposed to the fluid in the vessel 2. Alternatively, the coil 50 may comprise a tube with fins mounted preferably perpendicularly to the outer surface of the tube to increase the surface area.

[0103] The coil 50 is arranged to transfer heat from fluid stored in the vessel 2 to fluid pumped through the inside of the coil 50 tube. This may be for instance to transfer heat to potable water (e.g. to satisfy an immediate hot water demand) or to a fluid for space heating purposes (e.g. to satisfy an immediate space heating demand).

[0104] The inlet 52 to the coil 50 is located near the bottom of the vessel 2 and passes through the body of the vessel 2. The outlet 54 from the coil 50 is located near the top of the vessel 2 and passes through the body of the vessel 2. It will be appreciated however that the inlet 52 and outlet 54 may be routed through other surfaces of the vessel 2 e.g. through the lid 8. By extending the coil 50 substantially along the full height of the vessel 2, the efficiency of the heat transfer process from the fluid in the vessel 2 to the fluid in the coil 50 may be increased. Colder fluid enters the coil inlet 52 near the base of the vessel where the colder fluid stored in the vessel 2 is located. This keeps a low temperature difference between the two fluids, minimising the creation of entropy.

[0105] As the fluid passes through the coil 50, it rises vertically in the vessel 2 due to the orientation of the coil 50. The temperature of the fluid in the vessel 2 increases from the base to the top of the vessel 2 as in a traditional hot water tank, meaning the small temperature difference is maintained.

[0106] The fluid in the coil 50 then exits via the outlet 54 at the top of the vessel 2 where the fluid in the vessel 2 has the highest temperature, thus the water leaving the coil 50 also has a high temperature.

[0107] A small temperature difference reduces the rate of heat energy transferred between the fluid and the coil 50, thus the full height of the coil and the preferably corrugated or finned surface increases the surface area of the coil 50 sufficiently to be able to transfer heat at a suitable rate. This rate will depend on specific geometry and use of the heating system 100 but the heat transfer rate may be altered for instance by varying the coil 50 diameter, the vessel 2 height, or the number of coil 50 turns.

[0108] While not illustrated, various means of providing heat to the vessel 2 or drawing off heat from the vessel 2 may be included. This can include one or more device for providing heat to the vessel 2, and / or one or more further devices for drawing heat from the vessel 2. Suitable devices include for example an immersed heat exchanger and a heat exchanger external to the vessel. Suitable devices include further immersed coils, a plate heat exchanger, and an immersed electrical heating element. In an example a plate heat exchanger is immersed in an upper portion of the vessel 2 and a further submersible pump and conduits are provided for providing fluid from the vessel to the plate heat exchanger and back to the vessel. If the plate heat exchanger is intended to provide heat then fluid from the bottom of the vessel 2 can be drawn into the heat exchanger and it can be released back into the vessel 2 near the top of the vessel 2.

[0109] In the example illustrated in figure 1 an optional second coil 60 is shown disposed within an upper portion of the vessel 2.

[0110] The second coil 60 takes a similar form to the coil 50 in that it consists of a coiled hollow tube that allows fluid to flow within. An inlet port 62 to the second coil 60 and an outlet port 64 from the second coil 60 passes though the body of the vessel 2. Fluid flows into the inlet port 62, through the second coil 60 and out via the outlet port 64.

[0111] In an example the second coil 60 acts to provide a heat input to the fluid stored within the vessel 2. Heated fluid from an external heating device (for instance a heat pump, solar array, or fossil-fuel powered boiler) is pumped through the second coil 60, thereby transferring heat to the fluid stored in the vessel 2. The temperature of the fluid within the second coil 60 reduces accordingly and is returned to the external heating device via the outlet port 64.

[0112] In another example the second coil 60 acts to provide draw heat from the fluid stored within the vessel 2 for use in a space heating system. Fluid from an external space heating system is pumped through the second coil 60, thereby transferring heat from the fluid stored in the vessel 2. The temperature of the fluid within the second coil 60 increases accordingly and is returned to external space heating system via the outlet port 64.

[0113] The top up sub-assembly acts to quickly increase the temperature of the fluid in the top of the vessel 2.

[0114] When operating in a top up mode, the submersible pump 10 takes in fluid at the base of the vessel 2 and discharges it at the top of the vessel 2. In tandem, the electric heating element 30 is switched on and begins heating the fluid in the vessel 2 around the electric heating element 30. The fluid flowing out from the diffuser 14 displaces the heated fluid around the electric heating element 30, increasing the amount of heat transferred per second.

[0115] The controller controls the flowrate of the submersible pump 10 and the power output from the electric heating element 30. This allows the controller to adjust the rate of heat input to the vessel 2 and maximise heat transfer efficiency based on temperatures of the fluid within the vessel 2 (for instance the temperature at the base of the vessel, at the top of the vessel, or the degree of stratification within the vessel).

[0116] In an exemplary top-up operating mode, when the coil 50 is drawing heat from the fluid stored in the vessel 2, the controller may operate the top up sub-system to provide a rapid heat input to the system. This may involve operating the submersible pump 10 to pump cooler fluid from the base to the top of the vessel 2 which exits via the diffuser 14 in the vicinity of the electric heating element 30. The electric heating element 30 is turned on, thereby heating the fluid exiting the diffuser 14. This heat is transferred to the coil 50, the fluid in the vessel 2 then cools and descends to the base of the vessel 2 to be pumped back to the top of the vessel 2 again. The circulation of fluid via the top up sub-system ensures that there is a high rate of heat transfer when a sudden heat output from the vessel 2 is required.

[0117] The controller may be configured to perform the top-up operating mode in dependence on information received from the array of temperature sensors 20. When the quantity of heat stored in the vessel 2 is below a pre-determined threshold the controller may instigate the top-up procedure, thereby increasing the quantity of heat stored in the vessel 2.

[0118] Figure 2 shows a sectioned view of an exemplary embodiment of the heating system 100.

[0119] Figure 3 shows another heating system 200. The heating system 200 can generally include like features as the heating system 100, or it can include different features. The heating system 200 in particular includes a variant of the top up sub-system described with reference to the heating system 100.

[0120] In the variant shown, the top up sub-system further comprises a three-way valve 70 (also referred to as a three-port valve) in the outlet conduit 12. The three-way valve 70 is preferably an electrically controlled valve controlled by the controller.

[0121] In a first position, the three-way valve 70 connects the submersible pump 10 to the diffuser 14 via the outlet conduit 12 allowing the sub-system to top up the quantity of heat stored in the vessel.

[0122] In a second position, the three-way valve 70 connects the outlet of the submersible pump 10 to a drain port 72 that passes through the body of the vessel 2. When the submersible pump 10 is turned on, fluid from the submersible pump 10 is discharged externally from the vessel 2, thereby reducing the quantity of fluid in the vessel 2.

[0123] With the three-way valve 70 in the second position, the top up sub-system acts as a draining system to drain the fluid from the vessel 2. A hose or external pipework (not shown) may be attached to the drain port 72 to discharge fluid away from the vessel 2.

[0124] To drain the vessel 2, a user may input a command to the controller to drain the vessel 2. The controller then ensures the submersible pump 10 is not operating then sets the three- way valve 2 to the second position. Once this is achieved (for instance a feedback signal from the three-way valve 70 may inform the controller the second position has been achieved) the submersible pump 10 is turned on to pump fluid in the vessel 2 out through the drain port 72.

[0125] The controller may restrict draining of the heating system 200 e.g. if the fluid in the vessel 2 is above a pre-determined temperature to reduce the risk of scalding, or until detection of a drain hose attached to the drain port 72, or until input of heat to the vessel 2 is stopped. While the illustrated example shows the drain port 72 arranged in a side of the vessel 2, in an alternative example the outlet conduit 12 extends nearer the lid of the vessel 2 and the drain port 72 is arranged in a top of the vessel 2. In another alternative example the drain port 72 does not extend through the vessel wall, but is provided within the vessel (for convenience near the lid and easily accessible once the lid is opened) for attachment of a suitable conduit for draining.

[0126] In a variant the three-way valve 70 is manually actuable. In another variant instead of a three way valve a junction is provided in the outlet conduit 12, with one branch leading to the outlet of the outlet conduit 12, and the other branch leading to a sealable port. The sealable port can be adapted so that it can receive a conduit. Each branch can include a shut off valve to enable or prevent flow through either branch. A stopper can be inserted or a lid applied at the outlet of the outlet conduit 12 and / or the sealable port to enable or prevent flow through either branch.

[0127] In another variant the outlet conduit 12 is deformable, e.g. including a flexible portion, such that in a first configuration the outlet of the outlet conduit 12 can be arranged inside the vessel and in a second configuration the outlet of the outlet conduit 12 can be arranged outside the vessel. In this variant the outlet of the outlet conduit 12 may conveniently long enough to extend outside the vessel. The outlet conduit 12 may include a telescopically extendable portion. The outlet conduit 12 may include a concertina portion. Clips or brackets may be included to fix the outlet of the outlet conduit 12 inside the vessel 2 in an intended configuration. In the first configuration operation as a top-up sub-system can be provided, and in the second configuration operation as a drain system can be provided. In some examples the diffuser 14 described above is detachable from the outlet conduit 12 for ease of use during operation as a drain system.

[0128] In another variant the outlet conduit 12 includes an outlet port that can mate with a conduit extension such that the outlet of the conduit extension can be arranged outside the vessel. In some examples the diffuser 14 described above can mate with the outlet port of the outlet conduit 12 such that the diffuser 14 can be swapped for the conduit extension depending on intended use. The outlet port may for example include a quick coupling for ease of release and attachment of diffuser or conduit extension.

[0129] Figure 4 shows another heating system 300. The heating system 300 can generally include like features as the heating system 200, or it can include different features. The heating system 300 in particular includes a variant of the drain system described with reference to the heating system 200. In the variant shown, the three-way valve 70 (also referred to as a three-port valve) and the outlet conduit 12 are not part of the top up sub-system, but instead are part of another system for providing heat to the heat store fluid. The heating system 300 comprises a plate heat exchanger 80 that serves as a heat source to provide heat to the heat store fluid. A heat supply conduit 81 is arranged to provide heat transfer fluid from an external heat source to the plate heat exchanger 80, and a return conduit 82 is arranged to return heat transfer fluid from the plate heat exchanger 80 to the external heat source. The outlet conduit 12 and submersible pump 10 are arranged to provide heat store fluid from a lower portion of the thermal storage vessel 2 to the plate heat exchanger 80. A return section 84 returns heat store fluid from the plate heat exchanger 80 back to a region of the vessel (illustrated as an intermediate region, but different regions are suitable). A three-way valve 70 is provided in the outlet conduit 12 with a drain port 72 as described with reference to the heating system 200. The variants to the three-way valve 70 for enabling drain operation as described with reference to the heating system 200 may take the place of the three- way valve 70.

[0130] Figures 5A and 5B show a heating system 400 with a number of controller modules for controlling the heating system. The heating system 400 includes a vessel 108 for containing a heat store fluid. The heating system 400 may optionally include features as described above.

[0131] A heat pump 114 is arranged to provide heat to the vessel 108. A heat pump flow conduit 111 provides heated heat store fluid from the heat pump 114 to an upper portion of the vessel 108, and a heat pump return conduit 112 returns heat store fluid from a lower portion of the vessel 108 back to the heat pump 114. While not illustrated in the example, where the heat pump flow conduit 111 releases fluid into the vessel a diffuser may be provided to reduce mixing in the vessel. While not illustrated in the example, where the heat pump return conduit 112 draws fluid from the vessel a diffuser may be provided to reduce mixing in the vessel. Diffusers can serve thermal stratification in the vessel and reduce mixing when thermal energy is being provided by the heat pump.

[0132] A space heating system 115 is also arranged to receive heated heat store fluid from the heat pump 114 and return it back to the heat pump 114. The space heating system 115 typically includes radiators for space heating (not illustrated). In the illustrated example the heating system is in a parallel branch to the vessel and flow to one or the other or both can be controlled with suitable flow valves for example. In another example the heating system is in series to the vessel, for instance in the heat pump return conduit 112 returning heat store fluid from the vessel 108 back to the heat pump 114. A coil heat exchanger 160 is included for providing heat from heat store fluid in the vessel 108 to a flow of fluid in the coil, typically to transfer heat to potable water to satisfy a hot water demand. A cold supply conduit 162 provides a flow of fluid (such as potable water) to be heated coil inlet at a lower portion of the vessel. A hot outlet conduit 162 receives a flow of heated fluid (such as potable water) from the coil outlet at an upper portion of the vessel. In the illustrated example the coil heat exchanger 160 is shown immersed in the heat store fluid, but it may be arranged otherwise provided it is in thermal contact with the heat store fluid (e.g. embedded in a wall of the vessel or external to the vessel). The coil heat exchanger 160 serves to isolate the heat store fluid circulating between the heat pump and the buffer vessel from e.g. potable water from a mains supply which is to receive heat from the vessel before being distributed throughout the home. In some examples (e.g as shown in Figure 5B) a branch in the cold supply conduit 162 bypasses the vessel to supply fluid (e.g. potable water) to a thermostatic mixing valve 163 arranged in the hot outlet conduit 164. Such a bypass branch and thermostatic mixing valve can assist in providing hot water at a fixed temperature (typically 45°C or more).

[0133] In other examples the coil heat exchanger is replaced by a different heat exchanger for transferring heat to a flow of fluid, such as a plate heat exchanger inside or outside the vessel with a pump for pumping fluid from the vessel through the plate heat exchanger in order to heat the flow of fluid (such as potable water).

[0134] In the example illustrated in Figure 5A an electric heating element 130 is provided in an upper part of the vessel 108 for immersion in the heat store fluid. The electric heating element 130 can supplement the heat pump during periods of high demand or when weather conditions limit the heat pump’s performance significantly. In other examples two or more electric heating element 130 are provided in the vessel 108, e.g. one in an upper part of the vessel 108 and the second in a middle region of the vessel or in a lower part of the vessel. While not illustrated, the vessel 108 may include a temperature and pressure relief valve and / or an expansion vessel.

[0135] In other examples other rapid heat sources are included in addition to or instead of the electric heating element, including a gas fired heat source for example.

[0136] In the example illustrated in Figure 5B an electric heating element 132 is provided in the hot outlet conduit 164 instead of in the vessel 108 for immersion in the fluid. In this example the vessel 108 may not include a temperature and pressure relief valve and / or an expansion vessel.

[0137] An array of temperature sensors 120 is arranged to sense temperatures at different heights in the vessel. The array of temperature sensors 120 can permit detection of a temperature distribution of heat store fluid in the vessel (also referred to as thermal profile). In some examples the array of temperature sensors 120 may be replaced by a single temperature sensor and a model of a thermal profile that is adjusted based on the single sensor temperature measurements. In some examples the array of temperature sensors 120 may be replaced by temperature and flow sensors in the heat pump flow conduit 111 ; heat pump return conduit 112; cold supply conduit 162; and hot outlet conduit 162, along with a model of a thermal profile that is adjusted based on the temperature and flow measurements. In the illustrated example a plurality of sensors are arranged on the outer surface of the vessel, but temperature sensors may be arranged inside the vessel or embedded in a vessel wall, for example.

[0138] Optionally sensors may be included to measure temperature and / or flow rate in one or more of: heat pump flow conduit 111 ; heat pump return conduit 112; cold supply conduit 162; and hot outlet conduit 162. Such sensors can enable more accurate determination of thermal energy exchanges to and from the heat-pump and thermal exchanges to and from the flow in the coil heat exchanger 160 (e.g. potable water supply). Such thermal exchanges can alternatively be inferred solely by observation of the output of an array of temperature sensors 120.

[0139] A buffer control module 140 receives data from the array of temperature sensors 120 (or from other sensors quantifying thermal profile and thermal exchanges associated with the vessel). The buffer control module 140 provides control signals to the heat sources to the vessel, in the illustrated example to the electric heating element 130, 132 (whether in the vessel or in a conduit) and to a heat pump control module 150. The heat pump control module 150 can control operation of the heat pump 114 and provision of heat to the vessel and / or space heating system 115. While the illustrated example shows the buffer control module 140 and heat pump control module 150 as separate modules, they can alternatively be integrated in a single controller.

[0140] An optional energy system unit 150 provides e.g. measurement data or control signals to the buffer control module 140 that can affect operation of the buffer control module 140. For instance the energy system unit 150 can be a sensor or data source that indicates surplus grid energy or surplus photovoltaic energy (e.g. from local measurement of mains frequency or voltage, or from a remote data source such as a grid electricity provider). The energy system unit 150 can cause the buffer control module 140 to switch a heat source (e.g. electric heating element 130, 132 and / or heat pump 114) on or off e.g. in order to absorb surplus electric energy and store it as thermal energy in the vessel. The buffer control module 140 manages thermal buffering in the vessel for the heat-pump and space heating system and provides heat for producing hot water. The vessel can provide thermal inertia to the heat pump and space heating system and can assist preventing the heat pump from being operated on short cycles while maintaining space heating over a period of time. The vessel can also provide heat for de-frosting the heat pump during operation in cold / high humidity conditions. The buffer control module 140 controls the energy sources (e.g. electric heating element 130, 132 and / or heat pump 114) to maintain an adequate ‘useable thermal energy’ in the vessel in dependence on inputs quantifying thermal profile and / or thermal exchanges associated with the vessel and optionally external energy availability signals (from energy system unit 150). A ‘useable thermal energy’ in the vessel may be determined by a temperature distribution in the vessel alongside the heat transfer performance of the coil / plate heat exchanger. A ‘useable thermal energy’ in the vessel is a quantity of thermal energy above a specific threshold temperature. A ‘state of charge’ quantity is related to the ‘useable thermal energy’: the state of charge is the proportion of thermal energy held in the vessel relative to a maximum target thermal energy that can be contained in the vessel. The maximum target thermal energy may be lower than a maximum possible thermal energy: for instance it may be possible to heat the heat store fluid to a high temperature, but for the sake of system efficiency and to maintain a high coefficient of performance a lower maximum storage temperature is chosen.

[0141] Figures 6A, 6B and 6C show a schematic of a thermal storage vessel 108 and a temperature profile associated with a vessel and temperature measurements at different heights in the vessel. A lower part of the vessel contains cool fluid below a threshold temperature TT. At the level of the heat pump return conduit 112 the temperature of the heat store fluid is at about TT. Above the level of the heat pump return conduit 112 the temperature increases with height, in the indicate example reaching a maximum temperature of 50 °C around the middle of the vessel. In figure 6B the ‘useable thermal energy’ is available from heat store fluid at or above TT and is graphically indicated with hatching. A formula for quantifying a usable thermal energy Eu (J) in the vessel is: with m: mass of heat store fluid; Cp: specific heat of heat store fluid; T : temperature; Tthresh: threshold temperature above which thermal energy is useable for a specific purpose such as hot water, space heating, heat pump defrosting; where the T(x) temperature profile is integrated over the height of the vessel where the temperature is above the threshold temperature (T> Tthresh). In the illustrated example the proportion of useable thermal energy relative to the maximum target useable thermal energy (if the vessel content were heated as fully as possible to the maximum temperature of 50 °C), that is the state of charge, is relatively high, over 75%. In figure 6C traces of temperature over time (simulated) are shown for an array of 60 temperature sensors arranged to sense temperatures at different heights of the vessel. In the illustrated example the vessel initially contains uniformly heated fluid at 50 °C, that is, the state of charge is 100%; as time passes the vessel is gradually depleted of useable heat, and in the end contains uniformly cool fluid at 20 °C, that is, the state of charge is 0%. Heat is drawn from the vessel at a steady rate, and no heat is provided to the vessel during the observed period. The left-most trace is for the bottom-most temperature sensor that first observes a rapid drop of temperature, and the right-most trace is for the top-most temperature sensor that last observes a gradual drop of temperature.

[0142] The buffer control module 140 can include a model that predicts a heat demand. The model can for example be based on a user-input hot water requirement schedule, or it can be modelled from historical hot water demand data. With the predictive model, the buffer control module can determine at each point of time whether there is sufficient useable energy (energy which can meaningfully transfer heat to the potable water supply based on the relative temperature difference). With the usable thermal energy or the temperature profile and the predictive demand model, the buffer control module 140 can determine the optimal level of heat within the vessel. The buffer control module 140 can control the heat sources depending on usage requirements and risk of having insufficient capacity to satisfy all demand, but can also include factors to reflect performance tradeoffs for certain uses (e.g. less efficient performance of the heat pump as the average temperature in the vessel increases; e.g. a heat pump compressor running at full power will often deliver heat at a lower COP (coefficient of performance) than a heat pump compressor which is modulated down to for example 50% of its full power capability). For instance, the buffer control module can determine whether to use both the heat pump and electric heating element 130, 132 in tandem (during high demand scenarios) or the heat pump alone (which is more efficient). Furthermore, the buffer control module can examine the rate of loss of useable energy which can signal the presence of a draw event (where hot water is demanded from the system). The buffer control module can determine when a draw event is rapidly depleting available useable thermal energy and cause the both the heat pump and electric heating element 130, 132 to provide heat in tandem; the buffer control module can determine when a draw event has finished and switch back to using the heat pump only to save energy.

[0143] The buffer control module 140 can also factor the heat pump’s warm-up characteristics when determining how much power is required when heating the heat store fluid thus allowing a further level of control optimisation.

[0144] Figure 7 shows a control scheme. Data from an array of temperature sensors 120 (thermocline sensor) is received. A predictive demand model provides a prediction of heat demand (including one or more of: hot water demand; space heating demand; and heat pump defrosting demand). The buffer control module 140 determines from those inputs whether there is sufficient useable energy in the vessel to cover hot water requirements based on the predicted demand. In the determination of sufficient or insufficient thermal energy the buffer control module 140 can factor in transient response of the vessel. This determination is periodically repeated. If it is determined that there is not sufficient useable energy in the vessel to cover hot water requirements, then in response the buffer control module 140 causes the heat pump to start providing heat. The buffer control module 140 also determines whether a rate of change of the state of charge is above a threshold. If the state of charge is rapidly changing, and in particular decreasing, then an additional heat source can be switched on. In particular if the rate of change of the state of charge is above a threshold then the buffer control module 140 causes the electric heating element 130, 132 to provide heat as well, such that both the heat pump and electric heating element 130, 132 to provide heat in tandem. In another example if the rate of change of the SOC is above a threshold then the buffer control module 140 causes a further electric heating element to be switched on. If the rate of change of the state of charge is below the threshold then the buffer control module 140 continues to cause the heat pump only to provide heat. The transient response of the heat store fluid in the heat pump system loop (e.g. from sensors measuring temperature and / or flow rate in the heat pump flow conduit 111 and / or heat pump return conduit 112) can in addition be monitored to tune selection of a suitable threshold for determining whether dual heating or heat pump-only heating is implemented. This can for example permit the control to establish how responsive the heat pump is as heat source, and ensure the heat pump is switched on early enough e.g. to ensure a predicted heat demand can be met. Transient response of a heat pump can vary e.g. with season, time of day, outdoor conditions and other factors, so monitoring transient response from the heat pump can permit better control. The controller monitors whether there is sufficient useable energy in the vessel to cover hot water requirements based on the predicted demand, and responds to provide and optimise heat stored in the vessel. By consulting the rate of change of the state of charge the buffer control module 140 can cause more efficient heat to be provided from the heat pump, or more rapid heat to be provided from the heat pump and electric heating element 130, 132 in tandem.

[0145] Figure 8 shows a schematic of vessel state of charge (SOC) over time. In the illustrated example the vessel is initially at a state of charge of 100%, that is, the vessel holds that maximum target thermal energy. A draw event is initiated, for example by a user drawing hot water and causing flow through the coil heat exchanger 160, heating up the flow as it passes and decreasing the thermal energy stored in the vessel. As heat is drawn from the vessel and the state of charge of the vessel drops, the buffer control module 140 determines that the state of charge has dropped below the level required to cover predicted hot water requirements (in the illustrated example at around 50% SOC), and heating is initiated. In the illustrated example the buffer control module 140 determines the rate of change of the SOC and that it is above a threshold, i.e the SOC is decreasing rapidly, and consequently the buffer control module 140 causes the heat pump and the electric heating element 130, 132 to provide heat in tandem. In the figure the period with tandem heating is indicated with light grey shading. While the draw event continues, the electric heating element provides heat nearly immediately and starts to counteract the SOC decrease. The heat pump displays a transient response, and after a warm-up time also starts providing heat that counteracts the SOC decrease further. In the schematic the state of charge profile shows an abrupt change where the heat pump starts to provide further heat, but the change cause by the heat pump (and to a lesser extent the electric heating element) is typically gradual. In the illustrated example the state of charge continues to drop until the draw event ends, but in other examples the state of charge may remain level or increase depending on the magnitude of the draw event and the heat the heat pump and electric heating element can provide. After a time the draw event ends, in the example when the SOC is at a level of around 30%. If the heat pump and electric heating element had not been turned on the vessel would have been fully depleted of useable heat before end of the draw event. After the draw event is concluded the SOC begins to increase. The buffer control module 140 can determine that the SOC is increasing again, and can infer that the draw event has ended. The buffer control module 140 can determine that slower more efficient heating can be implemented, and switch the electric heating element off while the heat pump continues to provide heat (indicated with dark grey shading). The controller causes the heat pump to switch off such that a SOC of 100% is reached. In some examples this may involve determining a transient response when switching off and causing the heat pump to switch off such that a SOC of 100% is reached following switching off the heat pump.

[0146] By providing a buffer controller that monitors transient responses in the vessel a number of useful factors can be determined, including:

[0147] • Warm up time of the heat pump in dependence on current operating conditions;

[0148] • Rate of depletion of heat stored in the vessel;

[0149] • Start and end of a heat draw event;

[0150] These factors are particularly important in optimising heat provision to the vessel such that heat demands are covered and optimum heating can be provided. If the vessel were controlled simply to ensure a certain minimum SOC is maintained then this can result in excessive short cycles of operation of the heat pump, suffering an unfavourable coefficient of performance and reducing life expectancy of the heat pump. On the other hand if the vessel were controlled simply to avoid use of the heat pump until the SOC is at 0% then the system may for a period be unable to meet a demand for heat (e.g. for hot water), which is also to be avoided. The described control approach can find a balance between user convenience and optimum heating and use of the heat pump.

[0151] Transient responses in the vessel may be monitored and used to update the control parameters each time a transient response of a certain type is observed. For instance when the heat pump is switched on the transient response in the vessel is monitored and a current warm up time of the heat pump can be determined and used until a newer value is observed. Other transient responses in the vessel may be monitored and used to determine a response, for instance end of a draw event (which may the cause the buffer control module 140 to switch off an electric heating element) or rate of depletion of heat stored in the vessel (which may the cause the buffer control module 140 to switch on an electric heating element)

[0152] The controller and control method are described in the context of a vessel that is a heat store (for containing non-potable water at ambient pressure and with a heat exchanger for providing heat to e.g. a pressurised flow of potable water). It will be appreciated that the controller and control method can also be used in a vessel that is a hot water tank (for holding pressurised potable water) that can also store heat, and receive heat and buffer heat from a heat pump and / or space heating system.

[0153] Figure 9 illustrates an example heating system 500 with many of the features same as the heating system 400 described with reference to figure 5, and like features are indicated with like reference signs. The vessel 208 is a hot water tank for holding pressurised potable water and the heat exchanger for receiving heat from the heat pump 114 is external to the vessel. A cold supply conduit 262 in a lower portion of the vessel can provide pressurised potable water into the vessel and a hot outlet conduit 264 at an upper portion of the vessel can provide hot pressurised water from the vessel to a user. A plate heat exchanger 260 is included for receiving heat from the heat pump 114 and transferring it to water from the vessel 208. Conduits 266, 272, 276 provide a flow path from the vessel to the plate heat exchanger 260 and back to the vessel (with an optional upper return branch 276 and valve 278 for selection of a return branch). A pump 268 is provided to pump water in the conduits 266, 272, 276. Upper and lower electric heating elements 130, 230 are included. Baffles 212 in the vessel act to reduce mixing between water above the baffle and water below the baffle.

[0154] The buffer control module 140 receives data from the array of temperature sensors 120 (or from other sensors quantifying thermal profile and thermal exchanges associated with the vessel). The buffer control module 140 provides control signals to the heat sources to the vessel, in the illustrated example to the electric heating elements 130, 230 and to the pump 268 and the optional valve 278, as well as to the heat pump control module 150 for control of the heat pump 114 and provision of heat to the heat exchanger and / or space heating system 115. The buffer control module 140 controls the heat pump and the electric heating element 130 in dependence on data from the array of temperature sensors 120 as described above. The second electric heating element 230 can enable additional rapid heat input for more nuanced control of the amount of rapid heat provided to the tank. In an example only one electric heating element is switched on if the rate of change of the SOC exceeds a first threshold, and both electric heating elements are switched on if the rate of change of the SOC exceeds a second threshold. The buffer control module 140 controls the pump 268 to operate when heat is being received from the heat pump or when heat is being provided to the heat pump for defrosting.

[0155] The controller and control method are described with reference to figures 6A-8.

[0156] Figure 10 shows another heating system 500. Both heating system 500 and the proceeding heating system 600 can generally include like features as any of the heating systems 100-400, or they can include different features. The heating systems 500 and 600 in particular show variants with a plate heat exchanger 530.

[0157] The proceeding described features are common to both heating systems 500 and 600.

[0158] Rather than having a coil heat exchanger 160 disposed within the vessel 108 to transfer heat from heat store fluid contained within the vessel 108 to water flowing through the coil heat exchanger 160, the heating system 500, 600 has a plate heat exchanger 530 arranged to transfer thermal energy from the heat store fluid contained within the vessel 108 to water flowing through the plate heat exchanger 530.

[0159] The plate heat exchanger 530 comprises an inlet conduit for water to pass into the plate heat exchange 530 and an outlet conduit for the water thereby forming a secondary side of the plate heat exchanger 530; and an inlet conduit for the heat store fluid and an outlet conduit for the heat store fluid forming a primary side of the plate heat exchanger 530. As the two fluids flow through the plate heat exchanger 530, heat is transferred from the heat store fluid to the water, thereby increasing the temperature of the water.

[0160] In the illustrated example the plate heat exchanger 530 is shown mounted externally to the vessel 108. Whilst it will be appreciated that this can simplify the vessel 108 and makes servicing the plate heat exchanger 530 easier, the plate heat exchanger 530 could nonetheless be mounted within the vessel 108 to simplify plumbing of the heat store fluid.

[0161] A variable speed pump 540 is arranged to circulate heat store fluid from the vessel 108 through the plate heat exchanger 530 and back to the vessel 108. The variable speed pump 540 is controlled by the buffer control module 140 which may alter the speed of the variable speed pump 540 to vary the flowrate of heat store fluid and thereby the amount of heat transferred by the plate heat exchanger 530 to the water.

[0162] The variable speed pump 540 draws thermal store fluid from the top of the vessel 108, optionally through a diffuser to reduce mixing of the heat store fluid in the vessel 108. The drawn heat store fluid passes through the variable speed pump 540, through the primary side of the plate heat exchanger 530, then is reintroduced back into vessel 108 at the base of the vessel 108. An optional diffuser may be mounted in the outlet of the conduit expelling heat store fluid from the plate heat exchanger 530 to reduce mixing of the heat store fluid in the vessel 108.

[0163] Cold water from the cold water supply conduit 162 passes through a flow sensor 520, e.g. a flow switch, then into the secondary side of the plate heat exchanger 530. The flow sensor 520 is configured to communicate with the buffer control module 140 and inform the buffer control module 140 when cold water begins flowing into the plate heat exchanger 530. The flow sensor 520 may be a simple on / off sensor (such as a flow switch) that changes depending on whether fluid is flowing at the flow sensor 520, or it may further determine the flowrate of fluid flowing at the flow sensor 520. The buffer control module 140 can then activate the variable speed pump 540 to begin cycling thermal store fluid through the plate heat exchanger 530.

[0164] After the flow sensor 520 the cold water conduit splits (optionally), with one branch feeding the secondary side of the plate heat exchanger 530 and the other passing into the thermostatic mixing valve 163 (optional). The secondary side of the plate heat exchanger 530 discharges heated water via the hot outlet conduit 164 into the thermostatic mixing valve 163. In some examples the thermostatic mixing valve 163 is omitted and the cold water conduit feeds the secondary side of the plate heat exchanger 530, and the secondary side of the plate heat exchanger 530 discharges heated water to a hot outlet conduit.

[0165] Water flowing from the outlet of the thermostatic mixing valve 163 passes through a temperature sensor 510. The temperature sensor 510 determines the temperature of the water leaving the thermostatic mixing valve 163 and communicates this information to the buffer control module 140. The buffer control module 140 can then vary performance aspects of the heating system 500 to increase, decrease, or maintain the rate of heat transfer to the water flowing through the thermostatic mixing valve 163 to maintain a desired temperature. Such performance characteristics may include the speed of pumps, the amount of heat delivered by the heat pump 114, and whether to turn on any immersed or inline electric heaters.

[0166] The fluid outlet from the temperature sensor 510 feeds into an optional electric heating element 132 which may be used to further increase the temperature of the water leaving the thermostatic mixing valve 163.

[0167] To maximise the heat drawn from the thermal store fluid circulating through the plate heat exchanger 530, the variable speed pump 540 is preferably operated at the minimum flowrate required to achieve the desired outlet temperature. The outlet temperature is determined by the temperature sensor 510. The desired outlet temperature may for example be user selected, or selected fora particular use (hot water supply, space heating, heat pump defrosting). Operating the variable speed pump 540 at the minimum flowrate required to achieve the desired outlet temperature minimises the temperature of the heat store fluid returning back to the vessel 108, thereby maximising the amount of heat extracted from the heat store fluid.

[0168] The control regime can enable a more nuanced provision of heat at the plate heat exchanger: when a high flow of water is to be heated at the plate heat exchanger this control regime causes a different pump speed to be adopted than when a small flow of water is to be heated at the plate heat exchanger; this can prevent or reduce, when a small flow of water is being heated, excess heat to returned to the vessel (which may cause unfavourable thermal mixing in the vessel). In some examples the heating is controlled such that the thermostatic mixing valve 163 is not usually used to cool water, as water is provided at the desired temperature directly from the plate heat exchanger.

[0169] While the illustrated example provides at the secondary side of the plate heat exchanger a flow of water for hot water supply to a user, in other examples the secondary side of the plate heat exchanger may be for a flow of heat transfer fluid for transferring heat to e.g. a space heating system or for defrosting the heat pump.

[0170] The heat pump 114 is used to provide a thermal input to the thermal store fluid. A primary circulation pump 560 circulates heat store fluid between the heat pump 114 and the vessel 108. The primary circulation pump 560 may be a variable speed pump and may either be controlled by the heat pump 114 or by the buffer control module 140. The allows for the rate of heat transferred to the heat store fluid to be controlled, thereby allowing for maximising the efficiency of the heat pump 114.

[0171] An optional electric heater 550 is arranged between the outlet of the heat pump 114 and the vessel 108, thereby able to provide an additional heat input to the thermal store fluid if required. This optional electric heater 550 may be controlled by the buffer control module 140.

[0172] The outlet from the primary circulation pump 560 discharges near the top of the vessel 108. An optional diffuser may be mounted in the outlet discharging into the vessel 108 to reduce mixing of the heat store fluid as it re-enters the vessel 108. Heat store fluid is drawn from the vessel 108 into the heat pump 114 from near the bottom of the vessel 108.

[0173] In these embodiments, each vessel 108 features an array of temperature sensors 120 which function as previously described with respect to other heating system embodiments.

[0174] Although not shown, it will be appreciated that additional electric heating elements may be disposed within the vessel 108 or inline with any of the conduits forming part of the heating system 500, 600. These act to quickly transfer thermal energy to the heat store fluid surrounding or passing through them, thereby speeding up the response of the heating system 500, 600 to a sudden heat demand, e.g. a hot water draw event.

[0175] In use, upon detecting a hot water draw event from the flow sensor 520 the buffer control module 140 activates the variable speed pump 540 to deliver thermal store fluid to the plate heat exchanger 530, thereby transferring heat to the water flowing through the plate heat exchanger 530. Depending on the quantity of heat stored in the vessel 108 as determined by the array of temperature sensors 120, the buffer control module 140 may then additionally turn on the heat pump 114 and corresponding primary circulation pump 560, and / or optionally any inline or immersed electric heaters to supplement the heat input to the hot water being delivered to the user.

[0176] The heating system 500 is described herein as a volumiser arrangement, with the proceeding features specific to the heating system 500.

[0177] The return fluid path taking heat store fluid from the vessel 108 to the heat pump 114 passes through the space heating system 115. In this arrangement, the volume of the space heating system 115 is added to the flow path of heat store fluid transferring heat from the heat pump 114 to the vessel 108 and back again. This increases the total quantity of heat store fluid in use the heating system 500, thereby increasing the amount of thermal energy that can be stored by the heating system 500. This is particularly useful for bridging the time between a hot water draw event being detected by the flow sensor 520, and the heat pump 114 powering on to sustain the heat drawn from the heating system 500. This therefore reduces the chances of the heating system 500 not being able to deliver water at a desired temperature.

[0178] By arranging the space heating system 115 in the return path of the heat store fluid to the heat pump 114, the heating system 500 is relatively simple thereby allowing the buffer system to be retrofitted to a standard volumizer arrangement heating system.

[0179] Figure 11 shows another heating system 600. The heating system 600 is described herein as a hydraulic separation arrangement, with the proceeding features specific to the heating system 600.

[0180] In this embodiment, a second circulation pump 570 draws heat store fluid from near the top of the vessel 108 and passes it through the space heating system 115. A return conduit then returns heat store fluid from the space heating system 115 to near the bottom of the vessel, with an optional diffuser in the outlet to reduce the mixing of thermal store fluid returned to the vessel 108.

[0181] The heating system 600 therefore has separate heat store fluid loops for transferring heat from the heat pump 114 to the vessel 108, and for transferring heat from the vessel 108 to the space heating system 115. This allows for a disconnect between the heat delivered to the vessel 108 and heat delivered to the space heating system 115, thereby further improving efficiency of the system by better routing of heat store fluid.

[0182] Figure 12 shows test data for two different heating systems with a buffer: one using an immersed heat exchanger coil to transfer heat (diamond symbols) and the other using a plate heat exchanger (bar symbols), the results being plotted in graphs showing usable quantity of hot water (volume of water over 40°C, V40, in litres) and volumetric efficiency (in percent) against delivery flow rate (that is, rate at which hot water is drawn by a user, in litres per minute).

[0183] V40, the quantity in litres of useable hot water delivered above 40°C from a thermal store, may be defined as according to the following equation:

[0184] Where t is time during the test, m is the mass flow rate through the store, Tois the outlet temperature from the store, Tuis the useable temperature threshold (in this case 40°C) and Tcis the cold inlet temperature.

[0185] As shown in the first graph of figure 12, use of a plate heat exchanger 530 in a buffer vs a coiled heat exchanger delivered a higher quantity of usable hot water. The quantity of usable hot water also increased with increasing delivery flow rate, as did the performance gap to the coil heat exchanger, clearly showing the advantages of using a plate heat exchanger to transfer heat from the thermal store to potable water.

[0186] The second graph show the same results but expressed in terms of volumetric efficiency, where volumetric efficiency (Ke)may be defined as:

[0187] Where V40-maxcan be expressed as:

[0188] Where M is the mass of water in the buffer, THis the setpoint temperature when the store is full at one uniform peak temperature, and Tc-avgis the average cold inlet temperature during the test used to define 740.

[0189] Again, it is seen that the plate heat exchanger embodiment achieves a greater volumetric efficiency that is sustained across a range of flowrates.

[0190] In some examples the heating is controlled to achieve a high volumetric efficiency for a given desired target outlet temperature. This can be achieved by, as described above, operating the variable speed pump at a minimum flowrate required to achieve the desired outlet temperature, thereby minimising the temperature of the heat store fluid returning back to the vessel, reducing destratification in the vessel, and maximising the amount of heat extracted from the heat store fluid.

[0191] It will be appreciated that reference to a plate heat exchanger may also refer to any heat exchanger arranged to transfer heat between two flows, for instance a shell-and-tube heat exchanger.

[0192] It should be recognised that the described thermal storage vessels can be provided in any form, such as cylindrical or cuboidal.

[0193] The vessels described herein could similarly be used with other suitable heat storage materials, for example phase change materials or aqueous solutions or mixtures or nonaqueous liquids or other fluids.

[0194] While the examples described above mostly consider domestic heating systems, it should be recognised that the described thermal storage vessels can be used for thermal storage in other settings and systems.

[0195] Where the upper part of a feature (e.g. vessel, coil) is referred to, it should be appreciated that this may include near the top of the feature, an upper portion of the feature, a top portion of the feature, a top half, third or quarter of the feature (by volume or by height), with the feature in such orientation as it is intended to be installed for use. Where the lower part of the feature is referred to, it should be appreciated that this may include near the bottom of the feature, in a lower portion of the feature, or in a bottom half, third or quarter of the feature (by volume or by height), with the feature in such orientation as it is intended to be installed for use.

[0196] It will be understood that any of the sub-assemblies or components described herein may be used in any number and combination. 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.

[0197] Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

[0198] The term ‘comprising’ as used in this specification and claims preferably means ‘consisting at least in part of’.

Claims

1. Claims1. A heating system comprising: a vessel for containing a fluid for receiving or delivering heat; a heat pump arranged to provide heat to fluid of the vessel; an array of temperature sensors arranged to sense temperatures at different heights of the vessel; and a controller configured to: determine a thermal energy in the vessel in dependence on inputs from the array of temperature sensors; determine a transient response in the vessel in dependence on inputs from the array of temperature sensors; determine a predicted heat demand; and control operation of the heat pump in dependence on the thermal energy in the vessel, the transient response in the vessel and the predicted heat demand.

2. The heating system of claim 1 , wherein the transient response is in response to operation of the heat pump.

3. The heating system of claim 2, wherein the controller is configured to determine a time delay between switching the heat pump on and steady state provision of heat to the vessel based on inputs from the array of temperature sensors; and to control operation of the heat pump to meet the predicted heat demand in dependence on the time delay.

4. The heating system of any preceding claim, wherein the transient response is in response to an event drawing heat from the vessel.

5. The heating system of claim 4, wherein the transient response is a decrease of thermal energy in the vessel in response to an event drawing heat from the vessel.

6. The heating system of any preceding claim comprising a further heat source, optionally an electric heating element, wherein the controller is configured to control operation of the further heat source in dependence on a rate of change of the thermal energy.

7. The heating system of claim 6, wherein the controller is configured to control the further heat source to switch on when the rate of change of the thermal energy exceeds athreshold.

8. The heating system of any preceding claim, wherein the thermal energy in the vessel is a thermal energy above a threshold temperature.

9. The heating system of any preceding claim, wherein the vessel is a hot water tank or a heat store.

10. The heating system of any preceding claim comprising a heat exchanger, optionally arranged inside or outside the vessel, for receiving heat from the heat pump.

11. The heating system of any preceding claim comprising a heat exchanger, optionally arranged inside or outside the vessel, for providing heat to a flow of fluid.

12. The heating system of claim 10 or 11 , wherein the heat exchanger is a coil heat exchanger or a plate heat exchanger.

13. The heating system of any preceding claim, comprising one or more temperature and / or flow sensors in one or more conduits to or from the vessel.

14. A controller for a heating system with a vessel for containing a fluid for receiving or delivering heat, a heat pump arranged to provide heat to fluid of the vessel; and an array of temperature sensors arranged to sense temperatures at different heights of the vessel, wherein the controller is configured to: determine a thermal energy in a vessel in dependence on inputs from the array of temperature sensors; determine a transient response in the vessel in dependence on inputs from the array of temperature sensors; determine a predicted heat demand; and control operation of the heat pump in dependence on the thermal energy in the vessel, the transient response in the vessel and the predicted heat demand.

15. The controller of claim 14, wherein the transient response is in response to operation of the heat pump.

16. The controller of claim 15, configured to determine a time delay between switching theheat pump on and steady state provision of heat to the vessel based on inputs from the array of temperature sensors; and to control operation of the heat pump to meet the predicted heat demand in dependence on the time delay17. The controller of any of claim 14 to 16, wherein the transient response is in response to an event drawing heat from the vessel.

18. The controller of claim 17, wherein the transient response is a decrease of thermal energy in the vessel in response to an event drawing heat from the vessel.

19. The controller of any of claim 14 to 18 wherein the heating system comprises a further heat source, optionally an electric heating element, wherein the controller is configured to control operation of the further heat source in dependence on a rate of change of the thermal energy.

20. The controller of claim 19, wherein the controller is configured to control the further heat source to switch on when the rate of change of the thermal energy exceeds a threshold.

21. The controller of any of claim 14 to 20, wherein the thermal energy in the vessel is a thermal energy above a threshold temperature.

22. A method of controlling a heating system with a vessel for containing a fluid for receiving or delivering heat, a heat pump arranged to provide heat to fluid of the vessel; and an array of temperature sensors arranged to sense temperatures at different heights of the vessel, wherein the method comprises: determining a thermal energy in a vessel in dependence on inputs from the array of temperature sensors; determining a transient response in the vessel in dependence on inputs from the array of temperature sensors; determining a predicted heat demand; and controlling operation of the heat pump in dependence on the thermal energy in the vessel, the transient response in the vessel and the predicted heat demand.

23. The method of claim 22, wherein the transient response is in response to operation of the heat pump.

24. The method of claim 22 or 23, wherein the transient response is in response to an event drawing heat from the vessel.

25. The method of claim 24, wherein the transient response is a decrease of thermal energy in the vessel in response to an event drawing heat from the vessel.

26. The heating system of any of claims 1 to 13, comprising a plate heat exchanger for providing heat from the heat store fluid of the vessel to a flow of fluid and a pump configured to pump heat store fluid from the vessel to the plate heat exchanger and back to the vessel, wherein the controller is configured to determine a heat demand at the plate heat exchanger and control operation of the pump in dependence on the heat demand at the plate heat exchanger.

27. A heating system comprising: a vessel for containing a heat store fluid for receiving or delivering heat; a heat pump arranged to provide heat to heat store fluid of the vessel; optionally an array of temperature sensors arranged to sense temperatures at different heights of the vessel; a plate heat exchanger for providing heat from the heat store fluid of the vessel to a flow of fluid; a pump configured to pump heat store fluid from the vessel to the plate heat exchanger and back to the vessel; and a controller configured to: optionally determine a thermal energy in the vessel in dependence on inputs from the array of temperature sensors; determine a heat demand at the plate heat exchanger; and control operation of the pump in dependence on the heat demand at the plate heat exchanger and optionally the thermal energy in the vessel.

28. The heating system of claim 27, wherein the pump is a variable speed pump and the controller is configured to control a pump rate of the pump in dependence on the heat demand at the plate heat exchanger and optionally the thermal energy in the vessel.

29. The heating system of claim 27 or 28, wherein the controller is configured to determine a desired outlet temperature of the flow of fluid; and control the pump rate of the pump at a minimum pump rate for maintaining the desired outlet temperature of the flow of fluid.

30. The heating system of claims 27 to 29, comprising a temperature sensor for sensing an outlet temperature of the flow of fluid, and wherein the controller is configured to control the pump rate of the pump in dependence on the outlet temperature.

31. The heating system of claim 29, wherein the controller is configured to control the pump rate of the pump to minimise a difference between the sensed outlet temperature and the or a desired outlet temperature.

32. The heating system of claims 27 to 31 , comprising a flow sensor for sensing a flow of fluid at the plate heat exchanger, and wherein the controller is configured to switch the pump on when a flow of fluid at the plate heat exchanger is sensed.

33. The heating system of claim 32, wherein the controller is configured to control operation of the pump, optionally a pump rate of the pump, in dependence on a flow rate sensed at the flow sensor.

34. The heating system of claims 27 to 33, wherein the controller is configured to control operation of the pump to minimise a temperature of heat store fluid returning from the plate heat exchanger back to the vessel.

35. The heating system of claims 27 to 34 comprising a further heat source, optionally an electric heating element, wherein the controller is configured to control operation of the further heat source optionally in dependence on the thermal energy in the vessel.

36. The heating system of claims 27 to 35, wherein the plate heat exchanger is arranged inside the vessel or outside the vessel.

37. The heating system of claims 27 to 36 comprising a further heat exchanger, optionally a second plate heat exchanger or a coil heat exchanger.

38. The heating system of claims 27 to 37, wherein the flow of fluid is a flow of heat transfer fluid or a flow of potable water.

39. The heating system of claims 27 to 38, wherein the plate heat exchanger is arranged to provide heat to potable water and / or a space heating system.

40. The heating system of claims 27 to 39, wherein the vessel is a hot water tank or a heatstore.

41. A controller for a heating system with a vessel for containing a fluid for receiving or delivering heat, a heat pump arranged to provide heat to fluid of the vessel; a plate heat exchanger for providing heat from the heat store fluid of the vessel to a flow of fluid; and a pump configured to pump heat store fluid from the vessel to the plate heat exchanger and back to the vessel; wherein the controller is configured to determine a heat demand at the plate heat exchanger and control operation of the pump in dependence on the heat demand at the plate heat exchanger.

42. The controller of 41 , wherein the pump is a variable speed pump and the controller is configured to control a pump rate of the pump in dependence on the heat demand at the plate heat exchanger.

43. The controller of claim 41 or 42, configured to determine a desired outlet temperature of the flow of fluid; and control the pump rate of the pump at a minimum pump rate for maintaining the desired outlet temperature of the flow of fluid.

44. The controller of any of claims 41 to 43 wherein the heating system comprises a temperature sensor for sensing an outlet temperature of the flow of fluid, and wherein the controller is configured to control the pump rate of the pump in dependence on the outlet temperature.

45. The controller of 44, configured to control the pump rate of the pump to minimise a difference between the sensed outlet temperature and the or a desired outlet temperature.

46. The controller of any of claims 41 to 45 wherein the heating system comprises a flow sensor for sensing a flow of fluid at the plate heat exchanger, and wherein the controller is configured to switch the pump on when a flow of fluid at the plate heat exchanger is sensed.

47. The controller of claim 46, configured to control operation of the pump, optionally a pump rate of the pump, in dependence on a flow rate sensed at the flow sensor.

48. The controller of any of claims 41 to 47, configured to control operation of the pump to minimise a temperature of heat store fluid returning from the plate heat exchanger back to the vessel.

49. A method of controlling a heating system with a vessel for containing a fluid for receiving or delivering heat, a heat pump arranged to provide heat to fluid of the vessel; a plate heat exchanger for providing heat from the heat store fluid of the vessel to a flow of fluid; and a pump configured to pump heat store fluid from the vessel to the plate heat exchanger and back to the vessel; wherein the method comprises determining a heat demand at the plate heat exchanger and controlling operation of the pump in dependence on the heat demand at the plate heat exchanger.

50. The method of claim 49, wherein the pump is a variable speed pump and the method comprises controlling a pump rate of the pump in dependence on the heat demand at the plate heat exchanger.

51. The method of claims 49 or 50, wherein the heating system comprises a flow sensor for sensing a flow of fluid at the plate heat exchanger, and the method comprises switching the pump on when a flow of fluid at the plate heat exchanger is sensed.

52. A heating system comprising: a thermal storage vessel for containing a heat store fluid for receiving or delivering heat; a heating element arranged in an upper portion of the thermal storage vessel for immersion in the heat store fluid; a conduit with a pump arranged to draw heat store fluid from a lower portion of the thermal storage vessel and provide it to an upper portion of the thermal storage vessel; and a coil heat exchanger arranged for immersion in the heat store fluid and extending substantially along the height of the thermal storage vessel.

53. The heating system of claim 52, wherein at least a portion of the outer surface of the coil heat exchanger includes formations arranged to increase the surface area of the coil heat exchanger, preferably wherein the formations are corrugations and / or fins.

54. The heating system of claim 52 or 53, wherein the pump is a submersible pump arranged inside the thermal storage vessel.

55. The heating system of any of claims 52 to 54, wherein the heating element is an electric heating element.

56. The heating system of any of claims 52 to 55, further comprising a diffuser arrangedat an outlet of the conduit and configured to reduce a velocity of heat store fluid provided to the upper portion of the thermal storage vessel.

57. The heating system of any of claims 52 to 56, further comprising a baffle arranged at an intermediate height in the thermal storage vessel.

58. The heating system of any of claims 52 to 57, further comprising a second coil heat exchanger arranged within the thermal storage vessel.

59. The heating system of claim 58, wherein the second coil heat exchanger is arranged in an upper portion of the thermal storage vessel.

60. The heating system of claim 58 or 59, wherein at least a portion of the outer surface of the second coil heat exchanger includes formations arranged to increase the surface area of the second coil heat exchanger, preferably wherein the formations are corrugations and / or fins.

61. The heating system of any of claims 52 to 60, wherein the coil heat exchanger is arranged to receive heat from the thermal storage vessel.

62. The heating system of any of claims 52 to 61 , wherein the coil heat exchanger is arranged to provide heat to potable water and / or a space heating system.

63. The heating system of any of claims 52 to 62, wherein an inlet to the coil heat exchanger is arranged at a lower portion of the thermal storage vessel and an outlet from the coil heat exchanger is arranged at an upper portion of the thermal storage vessel.

64. The heating system of any of claims 52 to 63, further comprising a plurality of temperature sensors configured to determine a quantity of heat stored in the thermal storage vessel and / or a distribution of heat stored within the thermal storage vessel.

65. The heating system of any of claims 52 to 64, wherein the conduit is configurable into a drain configuration for expelling heat store fluid out of the thermal storage vessel.

66. A heating system comprising: a thermal storage vessel for containing a heat store fluid for receiving or deliveringheat; a heat source arranged in an upper portion of the thermal storage vessel to provide heat to the heat store fluid; and a conduit with a pump arranged to draw heat store fluid from a lower portion of the thermal storage vessel and provide it to the heat source or an upper portion of the thermal storage vessel; wherein the conduit is configurable into a drain configuration for expelling heat store fluid out of the thermal storage vessel.

67. The heating system of claim 65 or 66, wherein the conduit comprises a junction with a first branch arranged to provide heat store fluid to an upper portion of the thermal storage vessel and a second branch arranged to expel heat store fluid out of the thermal storage vessel.

68. The heating system of claim 67, further comprising a three-port valve at the junction for selection of the first branch or the second branch.

69. The heating system of claim 68, wherein the three-port valve is an electronically controlled three-port valve.

70. The heating system of claim 69, further comprising a controller configured to control the pump, the heating element, and the three-port valve.71 . The heating system of claim 65 or 66, wherein the conduit is deformable and configured to extend outside the thermal storage vessel in the drain configuration.

72. The heating system of claim 71 , wherein the conduit comprises a flexible portion.

73. The heating system of claim 65 or 66, wherein an outlet port of the conduit comprises a coupling for mating with a conduit extension.

74. The heating system of any of claims 66 to 73, wherein the pump is a submersible pump arranged inside the thermal storage vessel.

75. The heating system of any of claims 66 to 74, wherein the heat source is a heating element, preferably an electric heating element, and the conduit is arranged to provideheat store fluid to an upper portion of the thermal storage vessel.

76. The heating system of any of claims 66 to 75, wherein the heat source is a plate heat exchanger, preferably arranged inside the thermal storage vessel, and the conduit is arranged to provide heat store fluid to the plate heat exchanger.

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