GB2558357A

GB2558357A - Thermal transfer system

Info

Publication number: GB2558357A
Application number: GB1717111.7A
Authority: GB
Inventors: Garrett Roger; Findlay John; Leedham Paul; Richards Graeme
Original assignee: Hydro Water Man Solutions Ltd
Current assignee: Hydro Water Man Solutions Ltd
Priority date: 2016-10-18
Filing date: 2017-10-18
Publication date: 2018-07-11
Also published as: GB201617639D0; GB201717111D0

Abstract

A thermal transfer system including a subterranean cell having an impermeable lower surface 4, a heat exchanger 12, particulate material 18 and entry system 22 which may form drainage channels. An inlet chamber (330 fig.8) is connected to the entry system and an exit port (360 fig.8), which may be an over-flow pipe, is connected to an outlet chamber (340 fig.8). Upper surface 24 may be permeable or non-permeable whilst the lower surface may be flat (fig.4) or have trenches 10. A pump 350 may be used to pump water through the cell or to recirculate water between the exit and inlet chambers during periods of low rainfall. A water sensor may be connected to a recirculation controller for switching the recirculation pump on and off. The heat from the transfer system may be used with a compressor and an evaporator (42, 44 fig.11) to supply hot water to a building but by reversing the cooling may be provided.

Description

(54) Title of the Invention: Thermal transfer system Abstract Title: A geothermal heat transfer system (57) A thermal transfer system including a subterranean cell having an impermeable lower surface 4, a heat exchanger 12, particulate material 18 and entry system 22 which may form drainage channels. An inlet chamber (330 fig.8) is connected to the entry system and an exit port (360 fig.8), which may be an over-flow pipe, is connected to an outlet chamber (340 fig.8). Upper surface 24 may be permeable or non-permeable whilst the lower surface may be flat (fig.4) or have trenches 10. A pump 350 may be used to pump water through the cell or to recirculate water between the exit and inlet chambers during periods of low rainfall. A water sensor may be connected to a recirculation controller for switching the recirculation pump on and off. The heat from the transfer system may be used with a compressor and an evaporator (42, 44 fig.11) to supply hot water to a building but by reversing the cooling may be provided.

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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THERMAL TRANSFER SYSTEM

This invention relates to a thermal transfer system, and particularly, but not exclusively to a renewable thermal transfer system forming part of a renewable heating system. The heating system may be a system comprising a (closed loop) ground source heating and cooling system incorporating a Sustainable Drainage System (SuDS). The invention relates particularly to combined Sustainable Drainage System (SuDS) and renewable thermal transfer system forming part of a renewable heating system.

Ground source heating and cooling refers to the extraction and replenishment of low grade renewable heat from shallow excavations for the heating and cooling of buildings or other structures by converting the earth’s and the sun’s energy through the application of ground source heat pump (GSHP) technology.

Known ground source heat pumps fall into one of two general categories: open loop; and closed loop.

Open loop systems require connection to wells, pits or aquifers for example. At a smaller scale, a problem with open loop systems is that they tend to be very expensive to install, and are only viable where a suitable aquifer is present.

Closed loop systems are sealed systems often used in connection with boreholes, ponds and/or horizontal trenches and are much more widely applicable compared to open loop. Closed loop systems tend to be less expensive to install. In both types of system, the ground conductivity needs to be determined in order to design appropriate systems. Borehole systems are not always viable in terms of cost, or drilling rig access and can on occasion experience leaks that are difficult and expensive to rectify.

In a closed loop system having horizontal trenches, the cost of installation may be lower than for other configurations and the installation process is more straightforward. Both horizontal and vertical arrays of trenches may be used. It is possible to use either straight or coiled (slinky) heat exchange pipes in the trenches. By contrast, only straight pipe, can be used in boreholes.

There are no maps or databases available for research of ground (soil) thermal conductivity and so this soil property is rarely, if ever known. There is geological variability in the surroundings, and seasonal variability with regards to soil saturation and the water l

table. This means that ‘desk-top’ estimation of soil thermal conductivity cannot be achieved. Furthermore, trenches may require a lot of space. Also, existing methods of design and installation result in wide variations in the system co-efficient of performance (CoP) and seasonal co - efficient of performance (SCoP).

According to a first aspect of the present invention there is provided a thermal transfer system comprising a subterranean cell having a lower surface defined by an impermeable member;

a heat exchanger positioned within the cell; a particulate material through which the heat exchanger extends an entry system;

an inlet chamber operatively connected to the entry system; an exit port; and an outlet chamber operatively connected to the exit port.

In use, water enters the cell via the entry system, passes through the cell and exits via the exit port.

The inlet chamber serves to collect rain water or water falling from roofs of buildings before the water enters the cell by means of the entry system. The first chamber therefore serves to ensure a substantially steady flow of water through the cell. This feature may be particularly useful during periods where rainfall is low. Rain water that has been collected in the first chamber may be used to augment any rainwater falling onto the cell or may also be used when no rainwater falls onto the cell to maintain a substantially constant flow of water through the cell.

The outlet chamber is connectable to the exit port in order to collect water exiting the cell. Such water may then be allowed to discharge into a soak-away or other drainage system, for example, or maybe recirculated. This feature may be particularly useful for example during times when there is a heavier than usual rainfall. The second chamber allows water that has flowed through the system to be collected in the second chamber before eventually either soaking away or being recirculated as will be described in more detail below. This means that it is not necessary for all water to either soak away or be recirculated at the time that it exits the cell via the exit port.

The cell may be positioned at any convenient location. In embodiments of the invention the cell is positioned so that water running off a roof of a building will fall onto the cell and will thereby enter the cell via the entry system.

In embodiments of the invention the exit port comprises an overflow pipe.

Water may flow from the entry system to the exit port under the force of gravity.

In such embodiments of the invention, the lower surface of the cell may have a gradient of between about 0.05 to 0.025 so that the entry system is higher than the exit port. In such embodiments of the invention, water may flow through the cell under the influence of gravity.

In other embodiments of the invention, the thermal transfer system may comprise a first pump for pumping water from the entry system to the exit port.

In other embodiments of the invention the water may flow through the cell due to a combination of gravitational force and by means of pumping.

The first pump may form part of the thermal transfer system even in embodiments where the lower surface of the cell has a downward gradient from the entry system to the exit port.

Water entering the system via the entry system will flow through the subterranean cell before exiting the system. The presence of water flowing through the cell overcomes the disadvantages of existing, particularly horizontal, systems which are reliant on back-filled natural soil and the level of the water table in the surrounding ground. In addition, the flow of water through the cell increases the co-efficient of performance of the thermal transfer system.

In embodiments of the invention, the inlet and outlet chambers may be operatively connected to one another. In such embodiments, water exiting the cell via the exit port may be recirculated to re-enter the system via the entry system.

The inlet and outlet chambers may be operatively connected to one another by means of a recirculation conduit in the form of a pipe for example.

Embodiments of the thermal transfer system may comprise a second pump for pumping water from the second chamber to the first chamber.

As the water flows through the cell, energy from the water or a refrigerant mix circulating within the heat exchanger is transferred to or from the heat exchanger respectively before being transferred to a building or other structure that is to be heated or cooled by the thermal transfer system.

The thermal transfer system may comprise a recirculation controller for controlling operation of the recirculation pump. In such embodiments, when sufficient water falls on the cell and enters the cell via the entry system, it may not be necessary to operate the recirculation pump since sufficient water will be flowing through the cell from the entry system to the exit port.

However, during conditions of drought, or simply when insufficient water is falling onto the cell and entering the cell via the entry system, the recirculation controller can cause the recirculation pump to switch on, to thus pump water that has collected in the outlet chamber to the inlet chamber so that the water can again flow through the cell.

Under other circumstances it may be advantageous for the recirculation pump to operate even when sufficient water is entering the cell via the entry system.

Attenuated water that has flowed through the cell may thus recharge, or heat the ground within the cell. This may be particularly useful during prolonged dry periods.

In embodiments of the invention the recirculation controller comprises a sensor for sensing water entering the cell via the entry system. When there is sufficient water within the system, as sensed by the sensor, the controller can switch off the recirculation pump. Similarly, when the sensor detects that there is insufficient water within the system, the controller can switch on the pump to cause water to recirculate within the system.

The sensor may be any suitable sensor. In some embodiments, the sensor comprises a Expanding Disc Rain Water Sensor. This a control device that recognises the onset and cessation of precipitation. Sited in an exposed location, the sensor is hard wired via a timer to a logic controller configured so that the recirculation pump is activated in dry conditions only.

During weather conditions where too much water is entering the cell, water may exit the outlet chamber via the exit port which in some embodiments of the invention comprises an overflow pipe. Water exiting in this way may drain away into a nearby soak away.

Embodiments of the present invention may therefore be regarded as a combination of a geothermal heating system and a sustainable drainage system.

In embodiments of the invention, the cell is shaped to form an upper tray, a lower surface of which defines a lower surface of the cell. In embodiments of the invention the lower surface of the cell has a castellated configuration. In particular, the lower surface of the cell has a castellated trench configuration defining a plurality of trenches.

An advantage of this configuration is that when the cell is created, the tray may be initially formed by means of digging a pit in the ground where the cell is to be located. Trenches may then be formed at desired locations, thus reducing the volume of earth that needs to be removed compared to configurations where the cell has a flat lower surface.

The configuration also means that the cost of particulate material used to fill the cell is reduced.

The depth of the trenches may vary according to the prevailing conditions, but in some embodiments the trenches are between 0.7m and 1.5m deep.

The trenches may be spaced apart by any convenient distance, and in some embodiments the number of trenches and the length of each heat exchange pipe may be varied depending on the requirements of the thermal transfer system.

The width of each trench may vary between approximately 0.75m to 1.5m. The trough may be spaced apart such that there is a distance of between 2m to 4m between adjacent troughs.

The depth of the upper tray forming an upper portion of the cell may be any suitable depth, and may vary from between 0.3m to 0.6 m.

The impermeable member serves as a boundary between the cell and the surrounding soil. The impermeable member also prevents water that has entered the system from draining into the surrounding soil.

The impermeable member may take any convenient form, and in some embodiments of the invention, the impermeable member comprises an impermeable membrane.

The cell forming part of the thermal transfer system is filled with a particulate material. In some embodiments of the invention, the heat exchanger is positioned such that it extends through and is embedded by the particulate material which fills the entire cell.

The particulate material forms a load bearing foundation within the cell. Because a particulate material is used, voids exist between particles allowing water entering the system to fill the voids to thereby provide water storage and surround the heat exchanger. The particulate material thereby forms a porous ‘honeycomb’ structure.

In some embodiments of the invention, the particles forming the particulate material are of a substantially uniform size and/or type.

An advantage of such embodiments is that a single type of particulate material only may be used to fill the entire cell.

The heat exchanger may comprise a plurality of heat exchange pipes. In embodiments of the invention comprising a plurality of trenches, there may be one heat exchange pipe associated with each trench. In such embodiments, each trench may have a heat exchange pipe extending along its length and connected into common headers comprising supply and return fittings. The headers are then connected to an inlet side of a heat pump.

In some embodiments of the invention, the cell comprises an impermeable upper surface, and the entry system comprises a drainage channel.

The impermeable upper surface may extend across the entire cell, although in other embodiments the impermeable upper surface may extend only partially over the cell.

In embodiments of the invention there may be a plurality of drainage channels. The drainage channels extend through the impermeable upper surface to allow water to enter the cell. Once water has entered the cell it will flow into the voids between the particles forming the particulate material. This means that the heat exchange pipes which are surrounded by the particulate material will also, in use, be surrounded by water.

In some embodiments of the invention, the upper surface of the cell comprises a permeable surface extending over the cell. In such embodiments, the permeable surface itself acts as the entry system, since water will be able to pass through the surface and into the cell.

The heat exchanger may be formed from any suitable material. In some embodiments, the heat exchanger is formed from PEX cross-linked polyethylene. In embodiments of the invention comprising one or more heat exchange pipes, one or more pipes will be formed from PEX cross-linked polyethylene.

The heat exchanger may be formed from PEX-A, B or C, but in many embodiments the heat exchanger is formed from PEX-A cross-linked polyethylene.

A variety of different materials may be suitable for making the heat exchange pipes. However, PEX-A cross-linked polyethylene is the toughest plastic in common use. When pipes are made from PEX-A, the pipes can operate under pressure at a temperature of 100°C. PEX-A is highly resistant to extreme temperature fluctuations typically, this can range between -60°C and +100°C and chemical attack. The molecular structure of PEX-A is such that it has a very high resistance to sharp edge impingement as seen in its adopted jointing systems which could be experienced by the heat exchangers since the pipes are surrounded by the particulate material. PEX-A will also withstand a greater crush resistance in heavily compacted constructions and busy trafficked areas, i.e. car parks.

The heat exchange pipes may only be joined together by mechanical jointing based on the molecular memory characteristics. Such joints are able to withstand extremely large axial loads of tension and compression.

By means of these mechanical joints, the ground array of heat exchange pipes of appropriate length may be formed.

The joints may be located at the connection of an array of heat exchange pipes to its header and at the extension of an array of heat exchange pipes. The joints may also be used to allow for the inclusion of instrument and measurement probes.

The cell forming part of the thermal transfer system is connectable to a heat exchange system in order that the cell may be connected to a building or other structure to be heated or cooled.

In the specification the terms “heat” and “heating” are understood to mean also “cool”, “cold” and “cooling”.

According to a second aspect of the present invention there is provided a method of forming a thermal transfer system comprising the steps of:

forming a cell by creating a trough in the ground; lining the cell with an impervious member; installing a heat exchanger within the cell;

filling the cell with a particulate material such that the heat exchanger extends through the particulate material;

providing an entry system to allow water to enter the cell; providing an exit port;

providing an entry chamber operatively connected to the entrance system; and providing an exit chamber operatively connected to the exit port.

In embodiments of the invention the step of forming the cell comprises creating an upper tray having a lower surface defining a lower surface of the cell; and then forming spaced apart trenches in the lower surface of the cell.

The invention will now be further described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a perspective cut-away view of a cell forming a thermal transfer system according to an embodiment of the invention and having an impermeable upper surface;

Figure 2 is a perspective cut-away view of a cell forming a thermal transfer system according to another embodiment of the invention and having a permeable upper surface;

Figure 3 is a section of the castellated structure of the cell trenches of the cell shown in Figures 1 or 2 demonstrating a complete and consistent backfill of one material only;

Figure 4 is a schematic representation showing the shape of the trough that may be formed as an initial step to form the thermal transfer system of Figure 1 or Figure 2;

Figure 5a and 5b are schematic representation showing a trench formed in the trough of Figure 4 during formation of a thermal transfer system according to embodiments of the invention;

Figure 6 is a schematic representation showing dimensions ofthe trough and the trenches in embodiments of the invention;

Figure 7 is a schematic representation showing jointing for joining together the heat exchange pipes of Figure 1 or Figure 2;

Figure 8 is a schematic representation showing an embodiment of the invention having a recirculation system;

Figure 9 is a schematic view from above of the embodiment shown in Figure 3;

Figure 10 is a schematic representation showing the cell of Figure 1 or Figure 2 forming part of a renewable ground source system for heating and cooling a property and other structures.

Figure 11 is a schematic representation showing heat exchange within the system of Figure 10.

Referring initially to Figure 1, a subterranean cell forming part of a thermal transfer system according to embodiments of the invention is designated generally by the reference numeral 2. The subterranean cell 2 comprises a lower surface 4 comprising an impermeable membrane 6. The impermeable membrane prevents water from passing from the cell 2 into the surrounding natural soil 8.

The lower surface 4 of the cell has a castellated configuration defining trenches 10 which extend across the cell. The impermeable membrane serves to line each trench, so that any water held in the trenches will not be able to pass through the permeable membrane and into the surrounding soil.

The cell further comprises a heat exchanger 12 which, in this embodiment, comprises a plurality or array of heat exchange pipes 14. In this embodiment, each of the heat exchange pipes 14 is coiled, but in other embodiments, the heat exchange pipes could have a different shape.

The heat exchange pipes in this embodiment of the invention are made from PEX-A crosslinked polyethylene. The pipe has mechanical joints 60 shown in Figure 3 which serve to connect one length of pipe to another, and also to connect the heat exchangers to common headers.

The cell 2 is filled with a particulate material 18. In this embodiment, the particulate material 18 comprises a granular aggregate Type 3. Such an aggregate is defined as SHW Clause 805 Type 3 (open graded) Unbound Mixture. In this embodiment, the particulate material has a minimum of 30% void when compacted for use in the renewable collector and emitter system according to aspects of the present invention. Type 3 aggregate comprises angular stones that interlock with each other forming natural gaps that in assembly creating a porous and permeable honeycomb structure to enhance water flow through the cells.

The heat exchange pipes 14 are positioned such that they are surrounded by, and embedded in the particulate material.

The cell has an upper surface which in this embodiment is formed from an impermeable layer 24. The layer 24 extends over the cell 2. A tarmac I concrete layer 24 covers the layer 18 and forms a road, or car park for example.

The cell 2 further comprises drainage channels 22 which serve as an entry system and allow surface water to enter the cell 2 and to seep to the base of the cell forming a subterranean tank.

The cell 2 will be positioned so that rain water falling off roofs of structures such as houses, and other rain water can be collected. The rain water will enter the cell via the entry system, which in this embodiment comprises drainage channels 22. Once the rain water has entered the cell, it will be held in the trenches 10. Because the heat exchange pipes 14 are positioned within the trenches, during use of the cell 2, the heat exchange pipes will be constantly surrounded by water.

Referring now to Figure 2 a second embodiment of a cell forming a thermal system according to another embodiment of the invention is shown schematically. Parts of the cell shown in Figure 2 that are similar to parts of the cell shown in Figure 1 have been given corresponding reference numerals for ease of reference.

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Figure 2 shows a subterranean cell 200 having similar components to the components shown in the cell of Figure 1. However, in this embodiment, the upper surface 180 comprises a permeable layer 240 rather than an impermeable layer 24 as shown in Figure

1.

In this embodiment, the layer 240 serves as the entry system, since water may readily pass through the layer 18. In this embodiment therefore it is not necessary to have separate drainage channels.

Figure 3 shows a section through some of the castellated trenches 10 formed from a nonpermeable liner 6 as shown in Figures 1 and 2, filled with particulate 18. Diffusers 300 are located in base of each trench 10 and filter out impurities and leaves, for example.

A thermal transfer system according to embodiments of the invention may be made by initially digging out a trough shaped as an upper tray 400 as shown in Figure 4. Once the tray has been made, one or more trenches 10 may be formed by digging deeper down through a lower surface 410 of the tray as shown in Figure 5a. The trenches 10 have a lower surface 420 that defines a bottom surface of the cell.

Once the trenches 10 have been defined in the tray, an impermeable membrane 6 may be positioned to line the lower surface 410 and the trenches 10 as shown in Figure 5b.

The cell may have any desired dimensions, and in some embodiments, each trench has a width of between 0.75 m and 1.5 m, and the distance between adjacent trenches is between 2m and 4m. The depth of the tray is between 0.3m and 0.6m and the overall depth of the cell is between 0.75m and 1.5m. These dimensions are illustrated schematically in Figure 6.

Figure 7 shows in detail jointing system of heat exchange pipes 14, which in this embodiment are formed from PEX - A. PEX - A is a material with an enormously strong memory characteristic in that it will always attempt to restore its shape when disturbed. The jointing system makes use of this characteristic by belling out the pipe introducing a multi sharp edge circumferential metal ringed joint and allowing the PEX - A material to shrink over its surface. This results in a leak proof joint offering resistance to excessive axial loads.

Turning now to Figures 8 and 9, a schematic representation of a thermal transfer system according to another embodiment of the invention is designated generally by the reference numeral 800. The thermal transfer system 800 comprises a subterranean cell 2 as shown in Figure 2 having an inlet pipe 330 that directs water into inlet chamber 320. Collected rain water in inlet chamber 320 enters the cell 1 via conduit 310. A trickle flow transfer passes through the honeycomb structure of the cell releasing its heat to the refrigerated array of pipes 14. It is then collected into outlet chamber 340. In dry conditions this charge of water is available to be recycled back to reservoir 320 through pipe 370 for distribution into the cells. When rain water is in excess, exit to a drainage system is achieved through the overflow pipe 360.

The inlet 310 is connected to the inlet chamber 320 which collects rain water transferred from adjacent roofs directly into the chamber 320 or recirculated water entering the chamber via conduit 370. The water enters the cell 1 via the inlet 310 and passes through trenches 10 before entering the outlet chamber 340 having an overflow pipe 360.

During use of the thermal transfer system 800, rainwater that has been collected from, for example, a roof of an adjacent building in a normal manner by way of downspouts, is collected at inlet entry pipe 330 and directed into the inlet chamber 320. At the same time rainwater landing on a permeable car parking surface for example enters the cell via this permeable surface and makes it way to the base of the trenches 10. The head of water created in the inlet chamber 320 feeds into the base of the cell via the discharge entry pipe 310. Before water enters the discharge entry pipe 310 it passes through a filter diffuser 300 in order that for example leaves may be filtered out of the water.

In the embodiment of the invention the lower surface of the cell 1 has a downward gradient of between 0.05m to 0.025m from the entry system to the exit pipe 360. This enables a trickle flow of water to occur throughout the voids in a compacted type 3 stone. After filtration through a second diffuser 300 lower temperature water enters the outlet chamber 340 via pipe 390.

In dry conditions a trickle flow of water is still necessary. This is accomplished by recirculating water from the outlet chamber 340 back into the inlet chamber 320 via the return pipe 370 for regenerisation and discharge back into the cell 1.

A rainfall sensor switches off the recirculation pump 350 when there is sufficient rainfall, and switches the recirculation pump 350 on when there is insufficient rain.

When there is a deluge of water entering the cell 1, pipe 360 directs excess water into a nearby soak away.

Referring now to Figure 10, a heating/cooling system comprising the thermal transfer system 800 illustrated in Figures 8 and 9 is designated generally by the reference numeral 200. The heating and cooling system comprises subterranean cell 2 and a ground source heat pump (GSHP) 30.

The heating and cooling system 200 is operatively connectable to a building or other structure 32 which is to be heated and I or cooled by the thermal transfer system 300.

The GSHP 30 is connected to the building 32 by means of a flow pipe 38 and a return pipe 46. If the GSHP is located internally or the building 32, then pipe 38 and 46 will connect directly to the thermal system of that building, or other structure.

When the system 200 is used to heat the building or other structure 32, the inlet (supply) pipe 34, carries an antifreeze and water mixture or a refrigerant at around ground temperature, and return pipe 36 will direct the circulating fluid or refrigerant at a reduced temperature for re energisation back to a heat pump 30. The flow pipe 38, will deliver energised (elevated temperature) water from the heat pump to the house to release its heat to the building, then for the return pipe 46 to circulate the water back to the heat exchanger of the heat pump for re energisation. The system 200 can also be used to cool the building or other structure in which case the inlet and outlet pipes 38, 46 will carry chilled water. The outlet and inlet pipe 34, 36 of the ground array 14, will pick up the transferred heat from the house and will carry warmed antifreeze and water mixture or refrigerant to discharge the higher temperature energy to the ground.

Figure 11 shows further details of the heat system 200. As can be seen, the heating system 200 comprises a compressor 42 (increasing the temperature of the supply fluid from the inlet heat exchanger to the water in building) and an evaporator 44 (reducing the temperature of the heat pump refrigerant so as to be re charged from the ground temperature). The first heat exchanger 46, transfers heat from the ground and second heat exchanger 44 boosts the transfer to a higher temperature water for use in the building or other structure. By reversing the compressor and the expansion valve cycle the heat pump 30 producers chilled water to cool the building or other structure, and on this occasion warms the ground.

Claims

1. A thermal transfer system comprising a subterranean cell having a lower surface defined by an impermeable member;

2. A thermal transfer system as claimed in claim 1 wherein the exit port comprises an overflow pipe.

3. A thermal transfer system as claimed in claim 1 or claim 2 wherein the lower surface of the cell has a downward gradient from the entry system to the exit port of between 0.05m and 0.025m.

4. A thermal transfer system according to any one of the preceding claims comprising a first pump for pumping water through the cell.

5. A thermal transfer system according to any one of the preceding claims wherein the inlet and outlet chambers are operatively connected to one another.

6. A thermal transfer system according to any one of the preceding claims wherein the exit port comprises an overflow pipe.

7. A thermal transfer system according to any one of the preceding claims comprising a recirculation conduit connecting the first chamber to the second chamber.

8. A thermal transfer system according to any one of the preceding claims comprising a second pump in fluid communication with both the inlet chamber and the outlet chamber.

9. A thermal transfer system according to claim 7 or claim 8 comprising a recirculation controller for controlling recirculation of water within the cell.

10. A thermal transfer system according to claim 9 wherein the recirculation controller comprises a sensor for sensing water within the system, which sensor is operatively connected to a switch for switching the second pump on or off.

11. A thermal transfer system according to any one of the preceding claims wherein the cell comprises an upper portion shaped as a tray having a lower surface defining the lower surface of the cell.

12. A thermal transfer system according to any one of the preceding claims wherein the lower surface of the cell has a castellated trench configuration defining a plurality of trenches.

13. A thermal transfer system according to claim 12 wherein the trenches each have a depth between 0.7m and 1.5m.

14. A thermal transfer system according to claim 12 or claim 13 wherein each trench has a width of approximately between 0.75m and 1,5m, and adjacent trenches are spaced apart from one another by a distance of between 2m to 4m.

15. A thermal transfer system according to any one of claims 11 to 14wherein the depth of the tray forming the upper portion of the cell is approximately between 0.3m and 0.6m.

16. A thermal transfer system according to any one of the preceding claims wherein the cell comprises an impermeable upper surface, and the entry system comprises a drainage channel.

17. A thermal transfer system according to any one of the preceding claims wherein the entry system comprises a permeable surface extending over the cell.

18. A thermal transfer system according to any one of the preceding claims wherein the heat exchanger comprises a plurality of heat exchange pipes.

19. A thermal transfer system according to any one of the preceding claims wherein the cell is filled with a particulate material.

20. A thermal transfer system according to claim 19 wherein the particles forming the particulate material are of a substantially uniform size.

21. A method of forming a thermal transfer system comprising the steps of: forming a cell by creating a trough in the ground;

lining the cell with an impervious member;

5 installing a heat exchanger within the cell;

10 providing an inlet chamber operatively connected to the entrance system; and providing an outlet chamber operatively connected to the exit port.

22. A method according to claim 21 wherein the step of forming the cell comprises creating an upper portion of the cell in the form of a tray, a lower surface of the tray defining

15 a lower surface of the cell, and then forming spaced apart trenches in a lower surface of the tray.

Intellectual

Property

Office

GB1717111.7

1-22.