BACKGROUND TO THE INVENTION Aquaculture tanks are commercially used for growing tropical fish and crustaceans. Salt or fresh water contained within the tank is controlled within a specific temperature range, such as between 24 to 280C, so as to maximise the fish or crustacean growth rate.

Generally, temperature control of the salt or fresh wash in an aquaculture tank is achieved by an immersion element.

The immersion element is usually electrically heated which requires power generation by burning a fossil fuel.

Emissions resulting from combustion of fossil fuels are known to adversely affect the environment. Furthermore, fossil fuels are by their nature a limited resource and thus relatively expensive. Effective heating of an aquaculture tank consumes a relatively large amount of electricity and, therefore, is often not a commercially viable option.

Fish or crustaceans are typically grown in ponds, dams or other environments which are open to the atmosphere and surrounding ecosystems. Therefore, fish or crustaceans grown in these environments are at risk of disease or contamination. For example, fish grown in ponds can acquire a mud flavour and thus it may be necessary to expose them to a clean aquaculture environment before consumption. This is both generally inconvenient and expensive in such known aquaculture grow-out systems.

SUMMARY OF THE INVENTION An intention of the present invention is to provide a system for controlling the temperature of a liquid within a reservoir, said system being relatively efficient and inexpensive to operate.

According to one aspect of the present invention there is provided a system for controlling the temperature of a liquid within a reservoir, said system comprising: a collector designed to absorb heat from a solar or a waste heat source; one or more elements, each containing a phase change substance having a relatively high latent heat of fusion, located within a wall and/or floor of the reservoir and thus being in heat conductive communication with the liquid; and a heat transfer liquid recirculation system coupled between the reservoir and the collector, said recirculation system designed to recirculate a heat transfer liquid between the reservoir and the collector and thus transfer heat between the collector and said one or more elements whereby, in use, heat collected by the collector can be absorbed by the heat transfer liquid and transferred via the recirculation system to said one or more elements located within the reservoir, the heat transfer liquid fusing and thus charging the phase change substance which can thereafter be crystallised whereupon it releases its latent heat of fusion and thus heats the liquid in the reservoir thereby controlling the temperature of said liquid.

According to another aspect of the present invention there is provided a system for controlling the temperature of a liquid within a reservoir, said system comprising: a collector designed to absorb heat from a solar or a waste heat source;

a latent heat storage structure including one or more elements, each containing a phase change substance having a relatively high latent heat of fusion, said structure being in heat conductive communication with the reservoir; and a heat transfer liquid recirculation system coupled between the latent heat storage structure and the collector, said recirculation system designed to recirculate a heat transfer liquid between the latent heat storage structure and the collector and thus transfer heat between the collector and said one or more elements whereby, in use, heat collected by the collector can be absorbed by the heat transfer liquid and transferred via the recirculation system to said one or more elements located within the latent heat storage structure, the heat transfer liquid fusing and thus charging the phase change substance which can thereafter be crystallised whereupon it releases its latent heat of fusion and thus heats the liquid in the reservoir thereby controlling the temperature of said liquid.

Typically, the heat transfer liquid recirculation system includes one or more collector heat transfer tubes and one or more reservoir/storage structure heat transfer tubes designed to carry the heat transfer liquid through the collector and the reservoir/storage structure, respectively. Preferably, said heat transfer tubes are corrugated so as to maximise their surface area and thus increase heat transfer within the collector and the reservoir/storage structure.

Typically, the latent heat storage structure consists of a floor structure being designed to support the reservoir and thus being in heat conductive communication with the reservoir. Alternatively, the latent heat storage structure consists of a latent heat storage vessel housing said one or more elements, the storage vessel being in heat

conductive communication with the reservoir via a latent heat recirculation system.

Preferably, said one or more elements are set or formed within the wall and/or floor of the reservoir or the floor structure. Typically, said elements are at least partly encased within a first heat conductive layer of the wall and/or floor of the reservoir or the floor structure. More typically, said one or more reservoir/storage structure heat transfer tubes are also encased within the first heat conductive layer, said tubes being located adjacent and thus in heat conductive communication with said one or more elements. In one example the first heat conductive layer is constructed at least partly from a cementitious product.

Typically, a water impervious layer is formed on the first heat conductive layer immediately adjacent the liquid within the reservoir. The water impervious layer may consist of an epoxy-based resin, woven glass fibres or a combination thereof.

Advantageously, the epoxy-based resin provides a relatively smooth surface which alleviates the retention and build-up of contaminated solids or other matter on an internal surface of the reservoir.

Typically, an insulating layer is formed on a surface of the first heat conductive layer wherein said layer is sandwiched between the water impervious and the insulating layers. The insulating layer is constructed from a material being relatively lightweight and having high thermal insulation, such as foamed polystyrene.

Generally, the insulating, first heat conductive, and water impervious layers are supported or housed within a support structure. In one example, the support structure is partly fabricated from particle board.

Typically, the temperature control system further comprises an enclosing structure connected to the reservoir or the floor structure so as to define a substantially sealed space above the liquid within the reservoir, said space allowing for improved temperature control of said liquid.

In one embodiment, said structure includes a plastics sheet being coloured black on its internal surface and thus allowing for artificial control of light within the sealed space.

Typically, the heat transfer liquid recirculation system also includes a first recirculation pump coupled between said one or more collector tubes and said one or more reservoir/storage structure tubes, said pump being designed to recirculate the heat transfer liquid between the collector and the reservoir/storage structure. Preferably, the first recirculation pump is coupled to the collector and reservoir/storage structure tubes via a first recirculation line.

Typically, the temperature control system includes a controller operatively coupled to the first recirculation pump, the controller designed to actuate said pump so as to effect recirculation of the heat transfer liquid at predetermined temperature conditions in the reservoir and/or the collector. More typically, the control system includes a reservoir temperature sensor and a collector temperature sensor connected to the reservoir and the collector, respectively, said sensors also being operatively coupled to the controller so as to control the pump at predetermined differential temperatures.

In one embodiment, the pump is activated at a predetermined high differential temperature and deactivated at a predetermined low differential temperature. For example, the predetermined high and low differential temperatures may be approximately 40C and 20C, respectively.

Preferably, the reservoir temperature sensor deactivates the pump at a maximum temperature. In one example, the maximum temperature is from between approximately 26 to 280C.

Preferably, the collector consists of a plurality of collector panels depending on the amount of solar or waste heat available and the heat requirements of the reservoir.

Typically, the collector is an unglazed solar collector.

More typically, the solar collector comprises a base layer constructed from a thermal insulation material, and a second heat conductive layer formed thereon. In one embodiment, said one or more collector tubes are placed or laid on the second heat conductive layer.

Typically, the solar collector further comprises a heat absorbent layer formed on said one or more collector tubes and the second heat conductive layer, said absorbent layer being constructed of a material having relatively low radiation and reflectivity. In one example, the heat absorbent layer is constructed of a composite bitumen/latex based material.

Preferably, the temperature control system further comprises a liquid recirculation system coupled to the reservoir so as to effect recirculation of the liquid through the reservoir. More preferably, the liquid recirculation system includes a second recirculation pump designed to recirculate the liquid through the vessel. In one example, the recirculation system also includes a filter element designed to remove contaminated solids, such as food and other organic material, from the liquid within the reservoir.

Preferably, said one or more elements consist of a plurality of capsules designed to sealably contain the phase change substance. Typically, each of said capsules

contains from between 50 to 60 millilitres (ml) of the phase change substance. In one embodiment, the plurality of capsules are arranged as a strip of capsules located adjacent each other.

Typically, the phase change substance is a hydrate salt having a relatively high latent heat of fusion. More typically, the hydrate salt has a latent heat of fusion of approximately 79 Watt.hours/litre (Wh/l) and a melting point of approximately 290C. In one such example the hydrate salt is calcium chloride, hexahydrate (CaCl2.6H2O).

Typically, the temperature control system is used in an aquaculture installation for maintaining constant water temperature within a tank or reservoir. Thus, the system promotes the growth of fish and crustacean in an aquaculture installation.

BRIEF DESCRIPTION OF THE DRAWINGS In order to achieve a better understanding of the nature of the present invention a preferred embodiment of a temperature control system will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of a temperature control system; and Figure 2 is an exploded cross-sectional view of a portion of a reservoir.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in Figure 1 there is a temperature control system shown generally as 10 comprising a collector 12, a reservoir 14, and a heat transfer liquid recirculation system 16. The temperature control system 10 described is designed for use in an aquaculture installation for the growth of fish and crustaceans. The system 10 has been successfully trialled in an aquaculture installation for

growing black bream, this being somewhat surprising considering black bream are a non-tropical species of fish.

It should also be appreciated that the temperature control system is applicable for other uses where the temperature control of a liquid within a reservoir is necessary.

As illustrated in Figure 2, the reservoir 14 is formed in a number of layers, namely a water impervious layer 18, a first heat conductive layer 20, an insulating layer 22, and a supporting layer 24. In this example, the water impervious layer 18 is an epoxy resin coating which is formed on the first heat conductive layer 20 which is constructed from a cementitious product. The cementitious layer 20 is formed on the insulating layer 22 which in this example is constructed from a foamed polystyrene product.

The epoxy resin layer 18, cementitious layer 20, and polystyrene layer 22 are supported and housed within the supporting layer 24 which in this embodiment is constructed from particle board.

A plurality of elements 26 being designed to contain a phase change substance are set within the cementitious layer 20. The phase change substance of this embodiment is a hydrate salt consisting of calcium chloride, hexahydrate (CaCl2.6H2O) having a relatively high latent heat of fusion. However, it should be appreciated that other phase change substances or hydrate salts having relatively high latent heats of fusion may be appropriate depending on the temperature at which liquid within the reservoir 14 is to be controlled. The plurality of elements or phase change capsules 26 are formed as a strip of capsules located adjacent each other. Each strip of the phase change capsules 26 is approximately 1100 mm long and 255 mm wide.

The hydrate salt calcium chloride, hexahydrate has a melting or fusion temperature of approximately 290C and a latent heat of fusion of approximately 79 Watt.hours per

litre (Wh/l). It has been calculated that one (1) square metre (m2) of the phase change capsules 26 within the reservoir 14 will store approximately 660 Watt.hours (Wh) of energy over a temperature range of between 24 to 290C.

One (1) m2 of the phase change capsules 26 equates to approximately 7.5 litres of the hydrate salt calcium chloride, hexahydrate (CaC12.6H20). In the aquaculture installation described, the total surface area of phase change capsules 26 is approximately twenty four (24) m2.

Thus, the heat storage over a temperature range of between 24 to 290C is approximately 15.8 kWh.

Although not illustrated, the collector is a solar collector formed from a plurality of solar panels. Each of the solar panels is of a sandwich construction including a base layer and a second heat conductive layer formed thereon. A heat absorbent layer being constructed of a material having relatively low radiation and reflectivity, in this example a composite bitumen/latex base material, is formed on the second heat conductive layer. Each of the solar panels has a solar collector surface area of approximately two (2) m2 so that the total collector surface area is approximately forty (40) m2. It should be appreciated that the invention extends to solar collectors of various configurations and is not restricted to the particular construction described.

As depicted in Figure 2, the heat transfer liquid recirculation system 16 includes a series of collector heat transfer tubes 30 and a series of reservoir heat transfer tubes 32 both designed to carry a heat transfer liquid, in this example water, through the solar collector 12 and the reservoir 14, respectively. The collector and reservoir heat transfer tubes 30, 32 are corrugated so as to increase their available surface area. The corrugated tubes 30, 32 can also be bent around relatively tight corners without kinking. Approximately 120 metres (m) of collector heat

transfer tube 30 is provided for each solar collector panel, and approximately 210 m of reservoir heat transfer tube 32 provided in the reservoir 14.

In this example, the reservoir or tank 14 is approximately five (5) m in length, two (2) m in width and one (1) m in height giving a total tank surface area of approximately twenty four (24) m2. Thus, the tank 14 has a capacity of approximately 10,000 litres of liquid, in this embodiment either fresh or salt water. The reservoir heat transfer tubes 32 are arranged in three (3) parallel circuits within the tank 14. Two of the circuits are formed in the walls of the tank 14 and the other circuit formed in the floor of the tank 14. Each circuit occupies approximately eight (8) m2 of tank 14 surface area and includes approximately seventy (70) m of collector heat transfer tube 32 capable of containing approximately fourteen (14) litres of water.

As shown in Figure 2, the reservoir heat transfer tubes 32 for each circuit are set within the cementitious layer 20 adjacent the phase change capsules 26.

As illustrated in Figure 1 the heat transfer liquid recirculation system 16 also includes a first recirculation line 34 coupled between the collector and reservoir heat transfer tubes 30, 32. A first recirculation pump 36 is connected to the first recirculation line 34 so as to pump water between the solar collector 12 and the tank 14. For efficient operation of the solar collector 12 a flow rate of between 1.8 to 2.5 litres per minute (1/min) for every one (1) m2 of solar collector 12 area is used. These flow rates are based on Australian Standards for unglazed solar collectors. The normal operating pressure for water flowing through the first recirculation line 34 is approximately 294 kiloPascals (kPa) with a maximum pressure of approximately 343 kPa. A pressure release valve 38 may be connected to the first recirculation line 34 should the water pressure exceed the maximum pressure.

The temperature control system 10 also includes a controller shown generally as 40 being operatively coupled to the first recirculation pump 36. The controller 40 is designed to activate the pump 36 so as to effect recirculation of water through the solar collector 12 and the tank 14 at predetermined temperature conditions. A reservoir temperature sensor 42 and a collector temperature sensor 44 are located in the tank 14 floor and walls and the solar collector 12, respectively. The tank and collector sensors 42, 44 are electrically coupled to the controller 40 so that the first recirculation pump 36 can be controlled at predetermined differential temperatures.

The collector temperature sensor 44 wlll generally detect a higher temperature compared to the tank temperature sensor 42. The pump 36 is activated wher the collector and tank temperature sensors 44, 42 detect a maximum differential temperature of approximately 40C. The pump 36 is then deactivated once the collector and tank reservoir temperature sensors 44, 42 detect a minimum differential temperature of approximately 20C. The tank temperature sensor 42 also detects a maximum temperature within the tank 14 so as to deactivate the recirculation pump 36, via the controller 40.

Although not illustrated, the temperature control system preferably includes a liquid recirculation system, in this embodiment being designed to recirculate and filter fresh or salt water through the reservoir or tank 14. The recirculation system includes a recirculation line coupled to an inlet and an outlet of the tank 14. A second recirculation pump and a filter element are plumbed to the recirculation line, the filter element designed to remove contaminated solids, such as food and other organic matter, from the fresh or salt water within the tank 14.

The temperature control system may also include an enclosing structure which is designed to partly enclose the

reservoir or floor structure so as to define a sealed space above the liquid within the reservoir or tank. The sealed space permits more effective temperature control of liquid within the reservoir. Furthermore, in an aquaculture installation the enclosing structure may include a plastic sheet being coloured black on its internal surface whereby artificial control of light within the sealed space is possible.

According to another aspect of the present invention the capsules containing the phase change substance may be located within a latent heat storage structure. In one embodiment, the latent heat storage structure is a floor structure having the phase change capsules set or embedded therein. A reservoir or tank containing a liquid is then placed upon that portion of the floor structure in which the phase change capsules are set or embedded. The latent heat of fusion of the phase change substance is transferred to liquid within the reservoir or tank via a floor of the reservoir. Otherwise, the temperature control system is constructed similar to the temperature control system described above.

Alternatively, the latent heat storage structure may consist of a latent heat storage vessel housing one or more phase change elements, the storage vessel being in heat conductive communication with the reservoir via a latent heat recirculation system. The latent heat recirculation system includes a latent heat recirculation pump together with a latent heat recirculation line which is connected to both the reservoir and the latent heat storage vessel. The recirculation line is located within the wall(s) and/or floor of the reservoir. Thus, water recirculated through the latent heat recirculation system is heated by the latent heat of the phase change substance and thereafter the heated water heats liquid within the reservoir.

Operation of the temperature control system 10 described above will now be explained in some detail.

The solar collector 12 absorbs sunlight on its bitumen/ latex upper surface and transfers this solar energy to water contained within the collector heat transfer tubes 30. The solar heated water is recirculated through the reservoir heat transfer tubes 32 via the first recirculation line 34 and recirculation pump 36. The solar heated water passing through the reservoir heat transfer tubes 32 heats the phase change substance, in this example calcium chloride hexahydrate (CaCl2.6H20) having a melting point of approximately 290C, preferably melting or fusing and thus charging the phase change substance.

Generally in the evening the cooler fresh or salt water contained within the reservoir 14 cools the phase change substance via the epoxy resin layer 18 and cementitious layer 20 of the reservoir 14. As the phase change substance solidifies or crystallises it releases its latent heat of fusion thereby heating the fresh or salt water.

The phase change substance is then, during daylight hours, once again charged via solar heated water being recirculated through the recirculation system 16. Thus, the phase change substance contained within the capsules 26 undergoes a number of phase change cycles exchanging heat with the fresh or salt water in the reservoir and maintaining the temperature of the water in the reservoir 14. In this embodiment, where the phase change substance has a melting point of approximately 290C, the fresh or salt water temperature is maintained at a temperature of between approximately 24 to 280C.

The controller 40 together with the reservoir and collector temperature sensors 42, 44 and the recirculation pump 36 control recirculation of water through the solar collector 12 and reservoir 14. The temperature of the fresh or salt

water in the reservoir 14 is thereby maintained within the required temperature range.

The following data was empirically calculated for an aquaculture installation having a tank 14 surface area of approximately twenty four (24) m2 and a solar collector 12 surface area of approximately forty (40) m2. The aquaculture installation was otherwise constructed as described above.

TABLE 1 SOLAR COLLECTOR EFFICIENCY MONTH OF YEAR SOLAR COLLECTOR Q,,(MJ/m2) CONTRIBUTION (MJ) January 678.9 905.2 I February 535.5 714.0 I March 479.3 639.0 April 353.4 471.2 May 243.0 324.0 I June 204.6 272.8 11 July 220.8 294.5 11 August 276.7 369.0 ~ 11 September 390.6 520.8 October 492.7 657.0 November 588.2 784.3 December 657.9 877.3 TOTAL 5121.6 6829.1 Q is equivalent to the mean monthly global solar irradiation on a horizontal plane. These monthly Q values have been obtained from meteorological data provided for Perth in Western Australia.

It can be seen from the results of Table 1 that the solar energy collection efficiency for the system described is approximately 75%. That is, the solar collector is

relatively efficient. If necessary, heating provided by the solar collector 12 can be boosted by electrical heating. This will also depend largely on commercial considerations, such as the growth rate of fish or crustaceans achieved in an aquaculture installation including the temperature control system.

Now that a preferred embodiment of the present invention has been described in some detail it will be apparent to those skilled in the relevant art that the system for controlling the temperature of a liquid within a reservoir has at least the following advantages over the admitted prior art: (1) the temperature control system is relatively efficient using the latent heat of fusion of a phase change substance to control the temperature of a liquid within a reservoir; (2) the temperature control system is inexpensive to operate relying on solar or waste heat to melt or fuse the phase change substance; (3) the temperature control system is environmentally friendly not requiring the burning of a fossil fuel for power generation; and (4) the temperature control system can be adapted to provide a "clean" environment which is particularly suited to aquaculture installations.

Those skilled in the relevant arts will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. The elements containing the phase change substance may be of practically any shape and construction provided they contain the phase change substance and permit heat exchange with liquid within the reservoir. For example, the elements may consist of one or more pipes or tubes sealably containing the phase change substance, the pipes or tubes being set or located within the reservoir or floor structure. The specific construction of the reservoir or floor structure is not limited to the multi-layered sandwich construction described. For example, the reservoir may merely consist of a concrete-lined pond, the phase change elements being set within the concrete lining.

All such variations and modifications are to be considered within the scope of the present invention the nature of which is to be determined from the foregoing description.