WO2014049344A2

WO2014049344A2 - Thermal store

Info

Publication number: WO2014049344A2
Application number: PCT/GB2013/052493
Authority: WO
Inventors: John Thomason
Original assignee: Tbs Building Supplies Ltd
Priority date: 2012-09-26
Filing date: 2013-09-24
Publication date: 2014-04-03
Also published as: GB201217148D0; GB2506354A; WO2014049344A3

Abstract

A thermal store (100) has a heat storage unit (1) with a heat storage medium (2), a first heat exchange system (3) through which a high temperature fluid can be passed to transfer heat to the heat storage medium, and a second heat exchange system (28) for transferring heat from the heat storage medium to a target. The second heat exchange system includes a conductive heat transfer element (8) and a fluid circuit (11, fig. 9) for a heat transfer fluid operatively connected with the conductive heat transfer element (8). The thermal store has a control system (110, Fig. 9) operative to selectively change the second heat exchange system (28) between a conductive heat transfer configuration and a non-conductive heat transfer configuration. The control system may be operative to regulate the thermal store in order to ensure safe operation and to move the store between heat storage and heat transfer modes.

Description

Thermal Store

Technical Field of the Invention

The present invention relates to a thermal store and to apparatus and methods of conserving thermal energy that incorporate a thermal store. In particular, but not exclusively, the invention relates to a thermal store for a vehicle and to apparatus and methods of conserving thermal energy that incorporate a thermal store for a vehicle.

Background to the Invention

Road vehicles driven by fuel-burning internal combustion engines or electricity-consuming motors, such as motor cars or automobiles, generate a substantial amount of thermal energy which is wasted.

For example in a vehicle powered by an internal combustion engine, thermal energy generated by the engine is commonly dissipated in three different ways:-

(a) thermal energy removed from the engine by causing liquid coolant to flow through the engine is conveyed by the coolant to a radiator where it is discharged to atmosphere and to the vehicle interior heating system when in operation. Thermal energy may also be transferred to the engine oil and extracted from the oil circulation system by a suitable heat exchanger;

(b) thermal energy generated by the combustion process is discharged via an exhaust system to atmosphere;

(c) heat is dissipated from the surface of the engine and other heated parts, including the exhaust system, into the surrounding air mainly by convection.

Internal combustion engines are highly inefficient, as much as 65% of the energy produced by such an engine being dissipated as heat. There is also a substantial wastage of thermal energy in vehicles which have motors powered by electricity generated by hydrogen/oxygen regenerative fuel cells.

If the thermal energy generated by an internal combustion engine or other motor is to be used it can be used instantaneously, for example in well known combined heat and power units, or it can be stored for use at a time when it is required. A number of systems have been proposed for storing thermal energy on a motor vehicle for subsequent use in heating a target. In some cases, the stored thermal energy is used to heat a target on the vehicle such as the interior of the vehicle cabin. In other cases, the stored thermal energy is used to heat a target remote from the vehicle such as a hot water supply for a building. In most of the known systems, thermal energy from the coolant system and/or exhaust of an internal combustion engine is stored in a thermal store which uses water or a water/glycol solution as the storage medium. Water and water/glycol solutions are good for thermal storage and transfer as they have a relatively high heat capacity and low cost. However, the maximum temperature they can be raised to is relatively low, about 90 deg C or less.

One of the problems of storing thermal energy onboard a vehicle, is that the store itself is additional mass, and generally speaking the higher the mass or weight of the vehicle, the greater the fuel consumption. It is desirable then to keep the mass of a thermal store for a vehicle to a minimum. In addition, because space is usually restricted, the size of the thermal store must also be kept to a minimum, and be of a shape that can be fitted in to the vehicle body.

The amount of useful heat that can be stored in a single phase body of material can be found from the following equation: Heat = mass x specific heat of storage medium x temperature difference between the store and target heat use

Where the mass has to be kept low, it is advantageous to use a storage medium with a high a specific heat and for the temperature difference to be as high as possible. A thermal store capable of achieving a temperature range of 300/400 deg C will store more useful thermal energy in less space and mass, and is therefore a far more suitable store for use on vehicles than the more commonly known low temperature thermal energy stores. High temperature stores are also more effective as they can be used to raise the temperature of the target to a higher level. For example a thermal store at 90 deg C will only raise the temperature of the target to a lower value, typically 60 deg C. Thus high temperature stores have considerable advantages in terms of cost, efficiency and effectiveness. Further advantages can be gained by using a thermal storage medium which has latent heat capacity. EP1426601 discloses apparatus and methods for conserving thermal energy generated in a vehicle and which uses a thermal store capable of storing thermal energy at temperatures in the range of 300-400 deg C.

Whilst high temperature thermal stores offer many advantages for use on a vehicle over the more commonly used low temperature thermal stores, they present a problem when it comes to transferring thermal energy from the store to a target, which may be some distance from the thermal store. Typically, heat is transferred from a thermal store to a target using a heat transfer fluid, such as water or a water/glycol solution. The heat transfer fluid is passed through a circuit which includes a first heat exchanger associated with the thermal store in which heat is transferred from the thermal store to the heat transfer fluid and a second heat exchanger in which heat from transfer fluid is given up to the target. For use in low temperature thermal stores, the first heat exchanger may be in the form of a coil located within the thermal storage medium through which the heat transfer fluid is passed. However, this type of heat exchanger may not be suitable for use with a high temperature thermal store as the heat transfer fluid may be heated above its boiling point. In the case of water or a water/glycol solution for example, the fluid may turn to steam at high pressure which may be dangerous.

EP1426601 discloses an alternative heat transfer arrangement for a high temperature thermal store in which a conductive heat transfer block is clamped to the thermal store and a heat transfer fluid is passed through a coil in the heat transfer block. In the system disclosed, the heat transfer block is permanently connected by means of a fluid circuit with a remote target, such as the hot water tank of a building, and the block is clamped to the thermal store only when heat is to be transferred from the vehicle to the target. The use of a thermal heat transfer block avoids the need to have a heat exchange coil in the heat storage medium itself and avoids the need for a user to have to connect and disconnect the heat transfer fluid circuit but is limited in its application.

There is a need then for a high temperature thermal store which overcomes, or at least mitigates, some or all of the drawbacks of the known high temperature thermal stores.

There is a need in particular for a high temperature thermal store in which heat can be transferred from the store to a heat transfer fluid in a more effective and controllable manner than in the known high temperature thermal stores. Summary of the Invention

According to a first aspect of the invention, there is provided a thermal store having heat storage unit comprising a heat storage medium, a first heat exchange system through which a high temperature fluid can be passed to transfer heat from the high temperature fluid to the heat storage medium, and a second heat exchange system for transferring heat from the heat storage medium to a target, the second heat exchange system comprising a conductive heat transfer element and a fluid circuit for a heat transfer fluid operatively connected with the conductive heat transfer element, the thermal store having a control system operative to selectively change the second heat exchange system between a conductive heat transfer configuration and a non- conductive heat transfer configuration.

The control system may be configured to automatically switch the second heat exchange system between the conductive heat transfer and non-conductive heat transfer configurations in response to one or more inputs in accordance with one or more pre-defined algorithms.

The conductive heat member may comprise a conductive heat transfer surface, the store being configured such that when the second heat exchange system is in the conductive heat transfer configuration, the conductive heat transfer surface engages a thermally conductive surface region of the heat storage unit to establish a conductive heat transfer path between the heat storage medium and the conductive heat transfer element and that when the second heat exchange system is in the non-conductive heat transfer configuration a thermal break is located between the conductive heat transfer surface and the heat storage medium. The thermal break may be any one or more of a material of relatively low thermal conductivity, an air gap, and a vacuum.

The heat storage unit may have at least one conductive heat transfer region and at least one non-conductive heat transfer region, the conductive heat transfer element engaging a conductive heat transfer region when the second heat exchange system is in the conductive heat exchange configuration, the conductive heat transfer surface being positioned over a non-conductive heat transfer region when the second heat exchange system is in the non-conductive heat transfer configuration.

The heat storage medium may be a solid mass with a thermal break covering part of a surface of the heat storage medium to form the at least one non-conductive heat transfer region. The thermal break may be located in at least one recess in the surface of the heat storage medium so that the surface of the thermal break lies substantially level with the surface of the heat storage medium in adjacent conductive heat transfer regions. The heat storage unit may comprise a housing containing the heat storage medium, at least a portion of the housing being made of a thermally conductive material to form the at least one conductive heat transfer region, the conductive heat transfer surface engaging with a conductive heat transfer region of the housing when the second heat exchange system is in the heat transfer configuration. The housing may have at least one conductive heat transfer portion made of a material of relatively high thermal conductivity and at least one non-conductive heat transfer portion made of a material of relatively low thermal conductivity, the conductive heat transfer surface engaging with a conductive heat transfer region of the housing when the second heat exchange system is in the heat transfer configuration and being positioned over a non-conductive heat transfer region when the second heat exchange system is in the non- conductive heat transfer configuration.

Alternatively, the housing may be made of a material of relatively high thermal conductivity, such as metal, a material of relatively low thermal conductivity being positioned over at least a part of the housing to form the at least one non- conductive heat transfer region, an exposed region of the housing not covered with a material of relatively low thermal conductivity forming the at least one conductive heat transfer region. The housing may have at least one recess in which the material of relatively low thermal conductivity is positioned to form the at least one non- conductive heat transfer region. An outer surface of the material of relatively low thermal conductivity may lie substantially level with a conductive heat transfer portion of the housing adjacent the non-heat transfer region.

The conductive heat transfer element may be movable under control of the control system to switch the second heat exchange system between conductive heat transfer non-conductive heat transfer configurations. The thermal store may comprise an actuator for moving the conductive heat transfer element relative to the heat storage unit under control of the control system. The actuator may comprises an electric motor, electric actuator, pneumatic actuator or any suitable mechanical device for moving the conductive heat transfer element relative to the heat storage unit under control of the control system.

The thermal store may comprise a plurality of conductive heat transfer elements, each having a conductive heat transfer surface. The heat storage unit may have plurality of conductive heat transfer regions and non-conductive heat transfer regions, each of the conductive heat transfer elements being movable between a conductive heat transfer position in which its conductive heat transfer surface is in engagement with a corresponding one of the conductive heat transfer regions and a non-conductive heat transfer position in which its conductive heat transfer surface is positioned above a corresponding one of the non-conductive heat transfer regions.

At least part of the heat storage unit may be cylindrical, the conductive heat transfer elements being located about a cylindrical portion of the heat storage unit. In which case, the conductive heat transfer elements may be rotatable about an axis of the cylindrical portion of the heat storage unit between conductive heat transfer and non- conductive heat transfer positions. The store may comprise a rotatable cylindrical drive member mounted co-axially in spaced relation about the cylindrical portion of the heat storage unit, the conductive heat transfer elements being operatively connected with the drive member for movement therewith, such the conductive heat transfer elements can be moved between their conductive heat transfer and non-conductive heat transfer positions by rotation of the drive member. In an alternative embodiment, the conductive heat transfer elements may be movable in an axial direction of cylindrical portion of the heat storage unit between conductive heat transfer and non-conductive heat transfer positions. The conductive heat transfer elements may be planar and movable linearly relative to a planar surface of the heat storage unit between conductive heat transfer and non-conductive heat transfer positions. Where the thermal store has more than one conductive heat transfer element, all the elements may be movable synchronously between conductive heat transfer and non-conductive heat transfer positions.

A plurality of the conductive heat transfer elements may be interconnected by a material of relatively low thermal conductivity to form an integral conductive heat transfer member.

Each of the conductive heat transfer elements may be fluidly connected as part of the fluid circuit.

Fluid passages may be provided in the, or each, conductive heat transfer element, which passages form part of the fluid circuit.

The store may comprise a pump for circulating a heat transfer fluid through the fluid circuit, the pump being operative under control of the control system.

The control system may be operative to regulate the temperature of the conductive heat transfer element. The control system may be operative to switch the second heat exchange system between conductive heat transfer and non-conductive heat transfer configurations in order to regulate the temperature of the conductive heat transfer element. The control system may be operative to cause fluid to flow through the fluid circuit in order to regulate the temperature of the conductive heat transfer element. The fluid circuit may comprise a cooling heat exchanger for dissipating heat from the heat transfer fluid to atmosphere, the fluid circuit have a valve operative to connect the conductive heat transfer elements to the cooling heat exchanger.

The thermal store may comprise a burner for producing heat. The burner may be adapted to provide additional heat when the thermal store has been depleted. The first heat exchange system may be fluidly connected with an exhaust system of an internal combustion engine so that the heat from exhaust gasses of the engine can be transferred to the heat storage medium. The thermal store may be coupled with a catalytic convertor forming part of the exhaust system of the internal combustion engine. The coupling arrangement may be such that the thermal store maintains the temperature of the catalytic convertor and the second, conductive heat exchange system is operable to regulate the temperature of the catalytic convertor when the engine is running. The store may form a part of or be mounted to a motor vehicle. A vehicle included a thermal store in accordance with the first aspect as well as methods of operating a thermal store as described herein may also be claimed. In particular, methods of operating a thermal store as described below may be claimed

Detailed Description of the Invention

In order that the invention may be more clearly understood embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1 is a longitudinal cross sectional view through a first embodiment of a thermal store in accordance with the invention;

Figure 2 is a perspective, cutaway view of part of the thermal store of Figure 1;

Figure 3 is a lateral cross sectional view through the thermal heat store of Figure 1, illustrating the store with a second heat exchange system in a non- conductive heat transfer configuration; Figure 4 is a lateral cross sectional view through the thermal heat store of Figure 1, illustrating the store with a second heat exchange system in a conductive heat transfer configuration;

Figure 5 is schematic lateral cross sectional view through a second embodiment of a thermal store in accordance with the invention, illustrating the store with a second heat exchange system in a conductive heat transfer configuration;

Figure 6 is a view similar to that of Figure 5 but illustrating the store with a second heat exchange system in a non-conductive heat transfer configuration;

Figure 7 is schematic lateral cross sectional view through a third embodiment of a thermal store in accordance with the invention, illustrating the store with a second heat exchange system in a non-conductive heat transfer configuration;

Figure 8 is a view similar to that of Figure 7 but illustrating the store with a second heat exchange system in a conductive heat transfer configuration;

Figure 9 is a schematic representation of a fluid circuit forming part of a second heat exchange system of a thermal store in accordance with the invention;

Figure 10 is a longitudinal cross sectional view through a fourth embodiment of a thermal store in accordance with the invention incorporating a catalytic converter;

Figures 11a and l ib are a series of schematic views illustrating engagement between conductive heat transfer elements and heat transfer regions of a heat storage unit forming part of a thermal store in accordance with the invention in which the mating surfaces of conductive heat transfer elements and heat transfer regions are substantially parallel to one another; and Figures 12a and 12b are views similar to Figures 11a and l ib but illustrating an arrangement in which the mating surfaces of conductive heat transfer elements and heat transfer regions are substantially parallel are inclined relative to one another.

The invention will be described primarily in relation to several embodiments of a thermal store for use on a vehicle. However, it should be borne in mind that the invention is not limited to application with vehicles but can be equally applied to a thermal store wherever it may be advantageous to store heat generated by an internal combustion engine, motor or indeed any other source of relatively high temperature heat, e.g. electrical energy, for later use. The following description will focus primarily of details of the thermal store, its construction and operation rather than the target uses for the stored heat. However, for vehicular applications, typical target uses for the stored heat include targets external to the vehicle, such as heating water for a building, and target uses onboard the vehicle, such as preheating the engine. Other target uses to which the stored heat can be put include:

1) Cabin preheat on a motor vehicle.

2) Windscreen defrosting.

3) Cabin heating overnight, for example in cold climates such as Canada where lorry drivers sleep in their cabs during the night, and the cabin temperature needs to be maintained. This job is usually done by an additional fuel burning heater.

4) Engine anti-freeze means. In cold climates engine temperature must be kept above a minimum level e.g. -20 deg C. This is because the glycol in the coolant system will not be effective at very low temperatures. This is presently done by automatic engine start up and stop, additional fuel burning heaters, or by plugging in to an electrical power supply to provide heat by means of an electric immersion heater. 5) Coolant heating is required for engine and cabin use on hybrid and electric vehicles, as the heat produced by the electric motor is inadequate.

6) Coolant heating is also required where vehicles using start/stop technology, to supply heat to the cabin when the engine is stopped during a wait period.

7) Motorhomes. Heat can be used for space heating, hot water heating and cooking.

A first embodiment of a thermal store (100) in accordance with the invention is illustrated in Figures 1 to 4 and 9. The store includes an inner heat storage unit (1) having a cylindrical side wall (10) and containing a thermal storage medium (2). A first heat exchange system, indicated generally at (3), has an inlet (4) through which exhaust gases from the vehicles engine are directed through the heat storage unit (1) so as to transfer heat energy from the exhaust gases to the heat storage medium (2). The first heat exchange system (3) includes a shell and tube type heat exchanger within the heat store (1) and has an exhaust gas outlet (23) connected with a downstream portion of an exhaust system for the vehicle. An external bypass (5) may be fitted, so that the exhaust gases can be diverted away from the heat storage unit (1) once the store is up to its maximum permissible temperature by closing a heat storage unit inlet valve (6) and opening a bypass valve (7). In addition there are times when the exhaust gas temperature is lower than the temperature of the heat storage medium, in which case it is preferable to divert the exhaust gasses which would otherwise extract heat from the heat storage medium instead of charging it. An internal exhaust gas bypass arrangement can be used instead of an external bypass if desired.

Any suitable heat storage medium (2) can be used that is capable of safely storing thermal energy at temperatures in the range of 300-400 deg C. The heat storage medium may be a phase change material such as an organic salt with a high melting point of 150 to 200 deg, C, and a boiling point in excess of 400 deg C. Alternatively the heat storage medium may be a solid material such as is used in electric storage heaters. Where a solid material issued, the heat storage medium may not have to be contained within a housing (10). In this case, the conductive heat exchange elements may contact an exterior surface of the medium (2) directly in a conductive heat transfer configuration.

The heat storage unit (1) is contained within an outer housing (24). The outer housing may be made of a thermally insulating material so as to insulate the heat storage unit (1) to prevent the loss of heat from the store during the charge up period, and the time when the heat is discharged. It is important that this insulation is very effective, as for example when used for engine preheat, it may be 12 hours between parking the car at night, and leaving the following morning.

The thermal store (100) has a second heat exchange system, indicted generally at (28), and which is operative to transfer heat from the heat storage medium (2) to a target for use. The second heat exchange system (28) includes a number, in this case three but it could be more or less than three, conductive heat transfer elements (8) positioned externally of the cylindrical wall (10) of the heat storage unit (1). The conductive heat transfer elements (8) are made of a material having a relatively high thermal conductivity, such as a metal. As can be seen best in Figure 2, the conductive heat transfer elements (8) are elongate, extending over substantially the whole length of the cylindrical side wall (10) of the heat storage unit (1). The elements (8) are equi- spaced about the outer circumference of the cylindrical side wall (10) and the inner faces of the elements (8) are curved to match the contour of the cylindrical side wall (10) The inner faces of the elements (8) form conductive heat transfer surfaces that fit closely to the to the surface of the cylinder (10) so that heat is easily conducted from the heat storage unit (1) to the elements when the second heat exchanger is in a conductive heat transfer configuration, as will be described in more detail below.

The cylindrical wall (10) of the heat storage unit (1) is made of a material of relatively high thermal conductivity, such as a metal, and its outer surface is shaped to provide three elongate, equi-spaced, recesses extending along its length. An insulating layer (9) comprising a material of relatively low thermal conductivity is attached to the exterior of the wall (10) in each of the recesses. The insulating layers (9) are shaped so that their exterior surfaces are substantially continuous with the exterior surfaces of the un-recessed regions (36) of the cylindrical wall so as to form a substantially smooth cylindrical outer surface over which the conductive heat transfer elements (8) can be moved. The non-recessed regions (36) of the exterior surface of the heat storage unit

(1) will be referred to conductive heat transfer regions whilst the recessed regions covered by a layer of thermal insulation will be referred to as non-conductive heat transfer regions (38). The conductive heat transfer elements (8) are movable by rotation about the axis of the cylindrical wall (10) between a conductive heat transfer position in which each element overlies and contacts a respective one of the heat transfer regions (36) and a non-conductive heat transfer position in which each element (8) overlies a respective one of the non-conductive heat transfer regions (38). When the conductive heat transfer elements (8) are in the conductive heat transfer position, their inner faces contact directly the exterior of the non-recessed regions (36) of the cylindrical wall (10) of the heat storage unit. In this configuration, a conductive heat transfer path is established between the elements and the heat storage medium so that heat is able to transfer freely by means of conduction between the heat storage medium (2) and the conductive heat transfer elements (8) through the wall (10) of the heat storage unit (1). When in the non-conductive heat transfer position, the elements (8) are positioned over the non-conductive heat transfer regions (38). In this position the insulating material (9) acts as a thermal break in the conductive heat transfer path between the heat storage medium (2) and the inner, conductive heat transfer surfaces, of the elements (8). In this configuration, only a very small amount of heat is transferred from the heat storage medium (2) to the elements (8).

It will be noted from the above that even in the non-conductive heat transfer position, some heat will be transferred from the heat storage medium to the elements (8) due to the high temperature to which the heat storage medium can be raised. It will be appreciated therefore that the terms "conductive heat transfer" and "non- conductive heat transfer" are used in a relative rather than an absolute sense.

In order to prevent the elements (8) from damaging the insulation (9), guides (27) may be spaced along the length of the insulation over which the elements can ride as they move over the insulation (9). The guides can be made of a suitable hardwearing material with a relatively low coefficient of friction such as a metal, polymer or composite material.

When the heat storage medium (2) is being charged by the hot exhaust gas, or at other times when it is desirable to limit heat transfer to the conductive heat transfer elements (8), the conductive heat transfer elements (8) are moved to the non- conductive heat transfer position to place the second heat exchange system in a non- conductive heat transfer configuration. When the thermal store is an active heat transfer mode in which stored heat is being transferred to a target (Fig 9 12A/B/C), the elements (8) are moved by rotation to the conductive heat transfer position to place the second heat exchange system in a conductive heat-transfer configuration.

The second heat exchange system also includes a fluid circuit (11) operatively connected with the conductive heat transfer elements (8) through which a heat transfer fluid can be passed to transfer heat from the elements to a target. In the present embodiment, the fluid circuit includes pipes (21) attached to an exterior surface of each of the elements (8). However, in other embodiments fluid passageways (21) may be formed directly within the elements themselves. The fluid passageways (21) of all the elements are connected in series together by means of flexible pipes (40).

An embodiment of a fluid circuit (11) is illustrated in Figure 9 and the flow of fluid through the circuit (11) may be powered by an electric pump (13). The heat transfer fluid may be water or a water/glycol solution. The fluid circuit (11) may be part of or be operatively connected to the coolant system of the vehicle and the heat transfer fluid may be the same fluid used in the vehicle cooling system. A thermostat (14) may be fitted to the elements so that if the temperature should reach a predetermined level in the charge mode, then the fluid is circulated through the coolant circuit to transfer the excess heat to the engine coolant system, and thus be dissipated safely.

In the embodiment of Figure 1, the conductive heat transfer elements (8) are rotated between conductive heat transfer and non-conductive heat transfer positions by means of an outer drive cylinder (15). The elements (8) are mechanically linked to the drive cylinder (15), for example by rods (16). The drive cylinder is rotated by means of an electric motor and drive (not shown) or other mechanical means, in order to move the elements (8) from the conductive heat transfer position (36) to the non- conductive heat transfer position (38) and vice versa. The drive cylinder (15) may form part of the outer housing (24) or it may be located externally of the outer housing. In this case, slots are formed in the outer housing (24) through which the rods (16) extend.

Figures 5 and 6 illustrate a second embodiment of a thermal store (200) in accordance with the invention which is shown in non-conductive heat transfer and conductive heat transfer configurations respectively. The thermal store (200) is constructed and operated substantially the same as the first embodiment (100) described above. The only difference with the second embodiment (200) is that the conductive heat transfer elements (8) are formed as part of an integral cylindrical conductive heat transfer member (42) which incorporates thermally insulating portions (44) between the conductive heat transfer elements (8). The thermally insulating portions (44) are made of a material having a relatively low thermal conductivity and help to further thermally isolate the conductive heat transfer elements from the heat storage medium (2) when the second heat exchange system is in the non-conductive heat exchange configuration as shown in Figure 4. This embodiment also illustrates the use of fluid passages (21) formed integrally within the conductive heat transfer elements (8) and interconnected by flexible pipes (40).

A still further embodiment of a thermal store (300) is illustrated in Figures 7 and 8 which again show the store with the second heat exchanger in non-conductive heat transfer and conductive heat transfer configurations respectively. The thermal store (300) is constructed and operated substantially the same as the first embodiment (100) described above. The thermal store (300) according to the third embodiment differs from the previous embodiments in that the cylindrical wall (10) of the heat storage unit does not have recesses on is outer surface. Rather, the cylindrical wall (10) of the heat storage unit (1) has a plane cylindrical outer surface. Pads of thermally insulating material (9) are attached to the outer surface of the cylindrical wall (10) in discreet regions spaced about the circumference of the wall to form non- conductive heat transfer regions (38), whilst the portions (36) of the wall (10) that are not covered by the thermally insulating material form the conductive heat transfer regions. In this embodiment, the conductive heat transfer elements (8) must move radially inwardly and outwardly as well as rotationally as they move between a conductive heat transfer position in which their inner surfaces directly contact the exposed conductive heat transfer regions (36) as shown in Figure 8 and a non- conductive heat transfer position in which each element is located above a respective one of the thermally insulating pads (9). The elements (8) ride on pins (16) inserted in each end of the elements which rise and fall on a cam surface (26) on a cam plate (25) It will be appreciated that the drive mechanism which moves the elements (8) between conductive heat transfer and non-conductive heat transfer positions may included other mechanisms to raise and lower the elements (8) and that the elements may be biased radially inwardly to ensure they make firm contact with the conductive heat transfer regions (36) of the heat storage unit wall.

It will be appreciated that there are various ways in which the heat storage unit can be provided with conductive heat transfer regions (36) and non-conductive heat transfer regions (38). For example, the wall (10) of the heat storage unit itself may be constructed with some regions formed of a material with relative high thermal conductivity to form conductive heat transfer regions and other regions made of a material of relatively low thermal conductivity to form the non-conductive heat transfer regions without the need to attach a thermally insulating material to the exterior of the housing. Furthermore, where the heat storage medium (2) is a solid and no housing (10) is required to contain the medium (2), a thermally insulating material (9) can be attached to the exterior surface of the heat storage medium to form non- conductive heat transfer regions (38) whist conductive heat transfer regions (36) are defined by exposed areas of the medium not covered by insulation. The insulation (9) may be affixed in recesses formed in the outer surface of the medium (2) so that the elements (8) are able to move between conductive and non-conductive positions by means of rotation only.

There are also a variety of ways in which the conductive heat transfer elements can be moved between conductive heat transfer and non-conductive heat transfer positions The variations on this may be as follows:

1) Rotary method as described in the above, and as shown drawings as attached. 2) A longitudinal method where the heat conducting elements (8) are in the form of circular rings which move longitudinally (axially) forwards and backwards along the cylindrical wall (10) of the heat storage unit. In this case, the conductive heat transfer and non-conductive heat transfer regions of the heat storage unit are also provided in the form of alternate rings in or about the cylindrical wall (10).

3) The heat storage unit may not be cylindrical but may have planar faces. In this case, the conductive heat transfer elements (8) will also have a planar inner surfaces and may be moved linearly across the surface of the heat storage unit and/or up and down between conductive heat transfer and non-conductive heat transfer positions.

4) Any form of the above that moves the conductive heat transfer elements (8) between conducting or non-conducting positions by means of a method of propulsion such as an electric motor, electric actuator, or pneumatic actuator. It should also be understood that it not necessarily the conductive heat transfer elements (8) that must be moved relative to the heat storage unit (1). Rather, any suitable arrangement can be adopted that can be used to automatically change the second heat exchanger system between a conductive heat transfer configuration in which the conductive heat transfer elements (8) are in contact with a conductive heat transfer region of the heat storage unit to establish a conductive heat transfer path between the heat storage medium (2) and the elements and a non-conductive heat transfer configuration in which a layer or shield of thermally insulating material is positioned between the elements and the heat storage medium (2) to act as a thermal break, under the operation of a control system.

The design of a thermal store in accordance with the invention can be varied to suit its particular application. For example, a thermal store that is to be used only to provide engine preheat will differ in size and location from one which is intended to provide heat for external applications as well as or instead of engine preheat. In the former case, the store is most likely to be smaller and fitted beneath the vehicle as close to the engine as possible. In the latter case it will be larger and most likely fitted in the rear of the vehicle, either in the boot or below. Thermal energy from the thermal store (100, 200, 300) is only available once the vehicle has been driven and the store charged up. If however the vehicle has not been used for several days, the stored heat will have dissipated due to heat loss through the insulation or by conduction. It may be that in some applications heat must be available at all times, in which case there should be a means of obtaining heat from another source. An electrical heater connected to an external electrical supply may be used, as is already provided by manufacturers such as Kenlowe. Alternatively a fuel burning water heater such as is supplied by Webasto may be incorporated in the hydraulic system. For example, Figure 1 illustrates a novel method using a fuel burner (21) only, which may be incorporated into the exhaust system, so that the heat store can be charged up by burning fuel from the vehicle fuel tank.

Figure 9 illustrates schematically a typical fluid circuit (11) for use with a thermal store in accordance with the invention. In the fluid circuit (11) shown, connections are provided to allow the stored heat to be used for engine preheat (12A), vehicle cabin heating (12B) and external heating (12C). Circuit (11) includes a connector unit (46) to which hoses can be attached to connect the circuit to the external target (12C). The circuit also illustrates use of external heater (19) such as the Webasto or a Kenlowe electric heater to heat the fluid when the heat store is uncharged. It will be appreciated that the details of the fluid circuit can vary significantly from that shown depending on the particular application of the thermal store and the intended target uses of the stored heat.

The thermal store (100) includes a control system (illustrated figuratively at 110 in Figure 9) which automatically controls its operation, including movement of the conductive heat transfer elements (8) between their conductive heat transfer and non-conductive heat transfer positions, the flow of fluid through the fluid circuit (11), operation of the bypass valves (6, 7) as well as other aspects of the operation of the thermal store. The control system may include programmable controller and/or CPU and may include various sensors to provide input, such as temperature sensors for the conductive heat transfer elements and the heat storage unit. The control system may form part of or be connected with a control system for the vehicle.

Operation of a thermal store in accordance with the invention whilst fitted to a vehicle will now be described.

When the vehicle is running and the exhaust gases have reached a suitably high temperature, the heat storage medium (2) is charged. During charging, the second heat exchange system (28) is in its non-conductive heat transfer configuration in which the conductive heat transfer elements (8) are in the non-conductive heat transfer position. The exhaust gases are passed through the first heat exchange system (3) to charge the heat storage medium (2). The control system may monitor operation of the vehicle engine so as to automatically place the thermal store in a charging mode when the engine is running and the exhaust gases up to temperature.

During charging of the thermal store, the control system monitors the temperature heat storage medium (2). If the temperature of the heat storage medium reaches a predetermined upper threshold, the control system operates the valves (6, 7) to send the exhaust gases through the bypass. Should the temperature of the heat storage medium (2) subsequently fall below a predetermined lower threshold level during the same journey, the control system may again direct the exhaust gasses through the first heat exchanger (3). The control system continues to monitor the temperature of the heat storage medium and to direct the exhaust gases through the first heat exchanger (3) or the bypass (5) as required to ensure the storage medium is fully charged without exceeding the upper threshold temperature.

During charging, the control system also monitors the temperature of the conductive heat transfer elements (8) to ensure the temperature of the elements does not go above a predetermined maximum threshold, which will typically be in the region of 80 degrees Celsius. This is to ensure that the fluid in the circuit (11) does not boil. The control system may alternatively, or in addition, monitor the temperature of the fluid in the circuit (11). If the temperature of the elements/fluid reaches the predetermined threshold, the fluid circuit is connected with the cooling circuit of the vehicle so as to transfer the excess heat to the engine coolant system where it can be dissipated safely. This may be achieved by means of an electronically controlled valve which is operated by an electronic control system to selectively couple the fluid circuit (11) with the cooling circuit of the vehicle. Alternatively, the fluid circuit (11) may have a thematically controlled valve which opens automatically to connect the circuit heat transfer circuit (11) with the cooling circuit. The fluid may be circulated by means of the cooling circuit pump or the control system may activate the electronic pump (13). When stored thermal energy is to be transferred to a target, the thermal store is placed in an active heat transfer mode. The control system moves the conductive heat transfer elements (8) to the conductive heat transfer position to place the second heat exchange system in the conductive heat transfer configuration and activates the pump (13) to cause fluid to flow through the fluid circuit (11) between the conductive heat transfer elements (8) and the target (12A/B/C). Depending on the complexity of the fluid circuit (11), the control system may have to operate a number of valves to direct the fluid to the appropriate target or targets. Whilst heat is being transferred from the store to the target, the control system monitors the temperature of the conductive heat transfer elements (8) and/or the heat transfer fluid and if it rises above an upper threshold level will move the conductive heat transfer elements (8) back to the non- conductive heat transfer position until sufficient heat as been transferred to the target to bring the temperature back down to a lower threshold at which the elements (8) can be moved back to the conductive heat transfer position if required. The control system continues to monitor the temperature of the elements (8) and/or the fluid and move the elements between the conductive heat transfer position and the non-conductive heat transfer position as required maintaining a safe transfer of heat. The control system may also monitor the temperature of the target and modulate the elements (8) between the conductive and non-conductive positions and regulate the flow of fluid through the circuit (11) in order to bring the target up to a desired temperature and to maintain the temperature as required.

Depending on the target use of the stored heat, the control system may automatically commence and regulate heat transfer from the store in response to an input, such as from a timer or temperature sensor. The following are examples of typical target uses:

1. Engine preheat. This may be activated by a timer which the driver sets when he parks the vehicle, and he inputs the expected time of return. Alternatively an intelligent controller that monitors driver use and predicts the switch on time may be used.

2. Engine anti-freeze. A thermostat or sensor on the engine, or part of the vehicle that needs protection, is used to activate the thermal store to transfer heat to the engine until it reaches a predetermined temperature.

3. Fuel burning heaters. If the system is fitted with a fuel burning heater either in the circulation system or the exhaust system, a means of control will activate this when required.

External heat use. When the hoses are plugged in, there may be a switch sensor that detects that the hoses have been connected, and starts the heat transfer. In addition there may be a control means so that when the external target is fully charged, the heat transfer stops by moving to the non-conductive position. This is not only a functional requirement, but also a safety requirement so that the target does not overheat. 5. Hybrid and electric cars may have a control system that detects when there is insufficient heat for the cabin, and signals for additional heat to be transferred into the coolant system from the thermal store.

6. Cars fitted with engine start stop technology, may incorporate a signal that sends heat into the coolant system if the cabin heater is not receiving enough heat.

Other control features that may be included (though not limited by) for safe operation: a) The exhaust bypass valve may be opened when the store is fully charged, or when the exhaust gas temperature is lower than the store temperature. b) The fluid circuit may be switched on if there is heat leakage during the non conducting mode, which causes the conductive heat transfer elements to exceed a preset temperature e.g. 80 deg C. c) The exhaust gas bypass valve may also open if the conductive heat transfer elements overheat due to a failure of the means of moving the elements to the non-conducting position thus providing safety. This may be detected if the temperature exceeds e.g. 90 deg C, that is despite operation of the fluid circuit as in 7b above, the heat is still not being conducted away fast enough. d) A pressure sensor may be fitted in the exhaust system to detect unusually high back pressure and operate the exhaust bypass valves to direct exhaust gases through the bypass.

The mating surfaces of the conductive heat transfer elements (8) and the conductive heat transfer regions (36) may be substantially parallel to one another, or substantially co-axial in the case of curved surfaces. In this case, means may be provided to press the surfaces together to improve heat transfer between them. This may take the form of a spring or other bias arrangement to press the conductive heat transfer elements (8) into contact with the conductive heat transfer regions (36) when the second heat exchange system is in the conductive heat transfer configuration. Alternatively, the mating surfaces of the conductive heat transfer elements (8) and the conductive heat transfer regions (36) may be inclined relative to one another in the direction of relative movement between the two. The surfaces being arranged so that when a horizontal, or circumferential, force is applied to the conductive heat transfer elements to move them into engagement, movement of the inclined faces over one another produces a vertical, or radial, component of the force which presses the surfaces together.

This concept is illustrated schematically in Figures 11a, l ib, 12a and 12b. Figures 11a and l ib illustrate the relationship between conductive heat transfer elements (8) and their respective conductive heat transfer regions (36) in their non- conductive heat transfer and conductive heat transfer configurations respectively. In Figures 11a and l ib the conductive heat transfer elements (8) and the conductive heat transfer regions (36) have co-planar faces and are moved laterally (x) between conductive and non-conductive positions in response to the application of a horizontal force. In the conductive heat transfer position as shown in Figure 1 lb, an additional vertical clamping force is applied to press the conductive heat transfer elements (8) into close contact with the heat transfer regions (36) as indicated by the arrow (48). Figures 12a and 12b are similar to Figures 11a and l ib except that the mating surfaces of the conductive heat transfer elements (8) and the conductive heat transfer regions (36) are inclined relative to one another in the direction of movement (x) of the conductive heat transfer elements (8). In this case, when a horizontal force is applied to the conductive heat transfer elements (8) to move them into engagement with the heat transfer regions (36), movement of the inclined surfaces over one another produces a vertical component (50) of the horizontal force which acts to clamp the surfaces together. With this arrangement, an additional biasing or spring means to press the conductive heat transfer elements (8) into engagement with the heat transfer regions (36) may not be necessary, though of course such additional biasing or spring means could also be used if desired. Whilst Figures 11a, l ib, 12a, and 12b show planar conductive heat transfer elements (8) that are moved horizontally, it will be appreciated that the concept can be adapted for use where the conductive heat transfer elements and the heat transfer regions have curved mating surfaces, the elements being moved rotationally about an axis between conductive transfer and non-conductive heat transfer positions. The thermal store may be connected with a graphic or digital display to demonstrate to the driver how the system is operating at any time. It may, for example, give the driver an indication of the amount of heat generated by the system during operation. This may be important for external use of heat, if the amount of heat generated is a means of income from government subsidies. It may give indication of faults.

It is well known that the emissions from a catalytic converter are very high during the warm up phase, until the catalytic converter reaches its light off temperature of between 250 and 300 deg C after a few minutes. There are a number of methods that car manufacturers have used to try and raise the temperature of the catalytic converter as quickly as possible. In accordance with a further embodiment of the invention as shown in Figure 10 a catalytic converter (30) is attached to the thermal store (400) and is encapsulated in heat storage medium (31), which may be the same material (2) as in the heat storage unit (1), or may be a different material more suited to a higher temperature.

The catalytic converter (30) is thermally connected to the heat storage unit (1) so that any heat lost from the heat storage medium (31) about the catalytic converter can be replaced from the heat storage unit (1), thus extending the time-temperature retention of the catalytic converter.

The thermal store illustrated in Figure 10 is substantially otherwise the same as the previous embodiments except that the first heat exchange system (3) is a double pass heat exchanger, the flow of exhaust gases under normal operation being shown by arrows. This heat exchange arrangement incorporates an internal by-pass instead of the external by-pass (5) as illustrated in Figure 1. The bypass is activated by opening the exhaust valve (33) so that exhaust gases pass straight through the heat exchanger along a central passage (35) and out of the exhaust outlet (23). An external burner (21) as shown in Figure 1 may be included, but is not illustrated in this example. Since the internal surface area of the passageway (35) is very small, the amount of heat transferred to the heat storage medium (2) will be very small, which should not result in further overheating. However in some instances it may be necessary to line the inside of passage (35) to reduce the heat transfer even further. In order to prevent overheating of the catalytic converter, the conductive heat transfer circuit may be switched on and used to remove heat from the thermal store once it reaches a set temperature, e.g. 300 deg C. The heat removed from the thermal store is conducted away to the coolant system and discharged through the vehicle radiator. The exhaust by-pass can also operate at the same time, so that the heat transfer is only removing excess heat from the catalytic convertor.

All exhaust systems include a catalytic converter which is located in the exhaust system as close to the engine as possible. A thermal store in accordance with the invention for use in providing engine preheat, will also preferably be placed beneath the vehicle as close to the engine as possible. It is therefore possible to place the catalytic converter and the thermal store adjacent to each other as shown in Fig 10. In this case the catalytic converter is also encapsulated in heat storage medium, and insulated to prevent loss of heat. This will maintain the temperature of the catalytic converter for several hours after the vehicle has been parked. The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the invention. For example, whilst in the embodiments described a material of low thermal conductivity is used as a thermal break between the heat storage medium and the conductive heat transfer elements other forms of thermal break could be used. A thermal break could be provided by means of an element containing an air gap or a vacuum to reduce conductive heat transfer between the heat storage medium and the conductive heat transfer elements.

Claims

1. A thermal store having heat storage unit comprising a heat storage medium, a first heat exchange system through which a high temperature fluid can be passed to transfer heat from the high temperature fluid to the heat storage medium, and a second heat exchange system for transferring heat from the heat storage medium to a target, the second heat exchange system comprising a conductive heat transfer element and a fluid circuit for a heat transfer fluid operatively connected with the conductive heat transfer element, the thermal store having a control system operative to selectively change the second heat exchange system between a conductive heat transfer configuration and a non- conductive heat transfer configuration.

2. A thermal store as claimed in claim 1, in which the control system is configured to automatically switch the second heat exchange system between the conductive heat transfer and non-conductive heat transfer configurations in response to one or more inputs in accordance with one or more pre-defined algorithms.

3. A thermal store as claimed in claim 1 or claim 2, wherein the conductive heat member comprises a conductive heat transfer surface, the store being configured such that when the second heat exchange system is in the conductive heat transfer configuration, the conductive heat transfer surface engages a thermally conductive surface region of the heat storage unit to establish a conductive heat transfer path between the heat storage medium and the conductive heat transfer element and that when the second heat exchange system is in the non-conductive heat transfer configuration a thermal break is located between the conductive heat transfer surface and the heat storage medium.

4. A thermal store as claimed in claim 3, wherein the thermal break is selected from one or more of the group consisting of: a material of relatively low thermal conductivity, an air gap, and a vacuum.

5. A thermal store as claimed in any one of claims 1 to 4, wherein the heat storage unit comprises at least one conductive heat transfer region and at least one non-conductive heat transfer region, the conductive heat transfer element engaging a conductive heat transfer region when the second heat exchange system is in the conductive heat exchange configuration, the conductive heat transfer surface being positioned over a non-conductive heat transfer region when the second heat exchange system is in the non-conductive heat transfer configuration.

6. A thermal store as claimed in any one of the previous claims in which the conductive heat transfer element is movable under control of the control system to switch the second heat exchange system between conductive heat transfer non- conductive heat transfer configurations.

7. A thermal store as claimed in claim 6, wherein the store comprises an actuator for moving the conductive heat transfer element relative to the heat storage unit under control of the control system.

8. A thermal store as claimed in any one of claims 3 to 7, wherein store comprises a plurality of conductive heat transfer elements, each having a conductive heat transfer surface.

9. A thermal store as claimed in claim 8 when dependant on claim 5, wherein the heat storage unit has plurality of conductive heat transfer regions and non- conductive heat transfer regions, each of the conductive heat transfer elements being movable between a conductive heat transfer position in which its conductive heat transfer surface is in engagement with a corresponding one of the conductive heat transfer regions and a non-conductive heat transfer position in which its conductive heat transfer surface is positioned above a corresponding one of the non-conductive heat transfer regions.

10. A thermal store as claimed in claim 9, wherein at least part of the heat storage unit is cylindrical, the conductive heat transfer elements being located about a cylindrical portion of the heat storage unit.

11. A thermal store as claimed in claim 10, wherein the conductive heat transfer elements are rotatable about an axis of the cylindrical portion of the heat storage unit between conductive heat transfer and non-conductive heat transfer positions.

12. A thermal store as claimed in claim 10, wherein the conductive heat transfer elements are movable in an axial direction of cylindrical portion of the heat storage unit between conductive heat transfer and non-conductive heat transfer positions.

13. A thermal store as claimed in claim 9, wherein the conductive heat transfer elements are planar and are movable linearly relative to a planar surface of the heat storage unit between conductive heat transfer and non-conductive heat transfer positions.

14. A thermal store as clamed in any one of claims 8 to 13, wherein all the conductive heat transfer elements are movable synchronously between conductive heat transfer and non-conductive heat transfer positions.

15. A thermal store as claimed in claim 14 when dependent on claim 11, wherein the store comprises a rotatable cylindrical drive member mounted co-axially in spaced relation about the cylindrical portion of the heat storage unit, the conductive heat transfer elements being operatively connected with the drive member for movement therewith, such the conductive heat transfer elements can be moved between their conductive heat transfer and non-conductive heat transfer positions by rotation of the drive member.

16. A thermal store as claimed in any one of claims 8 to 15, wherein a plurality of the conductive heat transfer elements are interconnected by a material of relatively low thermal conductivity to form an integral conductive heat transfer member.

17. A thermal store as claimed in any one of claims 8 to 16, wherein each of the conductive heat transfer elements are fluidly connected as part of the fluid circuit.

18. A thermal store as claimed in any one of the previous claims, wherein fluid passages are formed in the, or each, conductive heat transfer element, which passages form part of the fluid circuit.

19. A thermal store as claimed in any one of the previous claims, wherein the store comprises a pump for circulating a heat transfer fluid through the fluid circuit, the pump being operative under control of the control system.

20. A thermal store wherein the control system is operative to regulate the temperature of the conductive heat transfer element.

21. A thermal store as claimed in claim 20, in which the control system is operative to switch the second heat exchange system between conductive heat transfer and non-conductive heat transfer configurations in order to regulate the temperature of the conductive heat transfer element.

22. A thermal store as claimed in claim 20 or claim 21, in which the control system is operative to cause fluid to flow through the fluid circuit in order to regulate the temperature of the conductive heat transfer element.

23. A thermal store as claimed in claim 22, where in the fluid circuit comprises a cooling heat exchanger for dissipating heat from the heat transfer fluid to atmosphere, the fluid circuit have a valve operative under control of the control system for selectively connecting the conductive heat transfer elements to the cooling heat exchanger.

24. A thermal store as claimed in any one of the previous claims, the store comprising a burner for producing heat.

25. A thermal store as claimed in any one of the previous claims, wherein the first heat exchange system is fluidly connected with an exhaust system of an internal combustion engine so that the heat from exhaust gasses of the engine can be transferred to the heat storage medium.

26. A thermal store as claimed in claim 25, wherein the thermal store is coupled with a catalytic convertor forming part of the exhaust system of the internal combustion engine.

27. A thermal store as claimed in any one of the previous claims, wherein, the store forms part of or is mounted to a motor vehicle.