FIELD OF THE INVENTION

This invention relates to a solar water heater and, more particularly, to a solar water heater that can be made at a low cost and that can therefore be suitable for use by persons unable to afford more sophisticated solar water heaters.

More particularly, but not necessarily exclusively, the invention relates to a solar water heater that can be used for heating water in batches and that does not need to be permanently connected to a mains water supply in order to fill it.

The scope of the invention is not, however, to be interpreted as being limited to low-cost solar water heaters or to water heaters that do not need to be permanently connected to a water supply.

BACKGROUND TO THE INVENTION

The heating of water utilising solar energy, especially for domestic purposes, is becoming increasingly important. This is so not only from the point of view of economy of operation, but also from the point of view of avoiding or decreasing the use of electricity that is associated with an appreciable carbon footprint.

Apart from this, electricity is not available to some persons living in rural or informal settlement areas and the availability of electricity is also not entirely dependable in many geographical areas. Numerous different designs of solar water heaters have been proposed and some of which are available on the market. However, most, if not all, of those that are available, are unaffordable to a market sector that lives frugally by force of circumstances.

Applicant perceives a need for a solar water heater that may be made in a more affordable form.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a solar water heater comprising, in an operative condition, a thermally insulated box having a translucent lid and an optionally removable container for water within the box wherein the container has at least one passage communicating with the interior thereof, the thermally insulated box being arranged such that water contained within a container positioned in use within the box becomes heated by solar energy that passes through the translucent lid in use, the solar water heater being characterised in that the container is translucent and a heat absorbing panel or layer is operatively present on the side of the container remote from the translucent lid of the box.

In a first variation of the invention the container is a collapsible container. In such an instance the collapsible container may be a flexible bag, conveniently a transparent bag. The flexible bag may have portions thereof that form two opposite, generally parallel, major surfaces of the bag connected together at spaced positions to limit their spacing when filled with water to thereby control the thickness of the filled bag in the manner of an inflatable mattress such as a lilo.

In a second variation of the invention the container may be of a relatively rigid material and may assume the form of a bottle such as a beverage or water bottle of a suitable size, typically a bottle having a capacity of from 1 to 5 litres, most commonly 1 .5 to 3 litres. Depending on the size of the containers there may be two or more containers that are preferably located parallel to each other in locating recesses provided in an insert positioned within the box. The insert is conveniently made of a foamed heat insulating material such as a foamed polystyrene or polyurethane with the recesses moulded into the foamed material. A space that creates an air gap to act as an insulation could also be employed. The bottle or bottles may conveniently be made of a polyethylene terephthalate (PET) material as this material is commonly used at the present time for the production of beverage and water bottles. Of course, any other suitable material can be used.

Further features of the invention provide for a heat absorbing panel that may be in the form of a single flexible sheet to be located between an inner surface of the container and a bottom of the box or insert; for the heat absorbing panel to be a suitable heat absorbing plastics material selected or treated to absorb energy of radiation passing through the lid and container and to transfer thermal energy absorbed by the heat absorbing panel by way of conduction or convection, or both, to the container and its contents; for there to be a layer of additional insulation between the container and inner surfaces of a bottom, sidewalls and end walls of the box or insert; and for there to be a single passage communicating with the interior of the container so as to serve both as an inlet and outlet according to requirements with a suitable closure optionally being provided for the passage, as may be required.

As an alternative to the heat absorbing panel, the container or containers may be provided with a heat absorbing layer applied to what is an operatively inner surface thereof in use so that solar radiation can be absorbed by the layer and transferred to the contents of the container by conduction and convection. Still further features of the invention provide for the box to be made of a fluted, weather resistant sheet material such as a fluted extruded plastics sheet material having multiple parallel elongate voids formed between parallel integral webs of material extending between what is in effect two surface sheets of the fluted sheet material or, alternatively, for the fluted sheet material to be a suitably weather resistant sheet of corrugated cardboard; for the box to be either folded from a single sheet of material or for the box to be composed of multiple panels fitting into slots extending along extruded corner connectors; for the box to have a stay associated with it for supporting an upper end region thereof with the box in an inclined position so as to face the sun in a generally north or south direction at the appropriate angle according to a time of year, in use; and for the solar water heater to have a graphic associated with it for indicating a preferred angle of inclination according to a time of year and degree of latitude at which the solar water heater is being used.

The lid may have two spaced parallel sheets of transparent material held in spaced relationship either by a peripheral frame, or by way of suitable spacers located between them, or both.

In order that the above and other features of the invention may be more fully understood, one embodiment of each variation of the invention and variations thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:-

Figure 1 is a somewhat broken away schematic side view of one embodiment of solar water heater according to the first variation of the invention; Figure 2 is a cross-section thereof taken a long line 11 - 11 in Figure 1 ;

Figure 3 is a cross-section of one side thereof taken a long line III - III in Figure 1 and showing a single communication passage attached to the bag;

Figure 4 is an enlarged section taken a long line IV - IV in Figure 2 showing the cross-sectional configuration of the extruded fluted sheet material from which the box is made;

Figure 5 is a cross-section of one side of an alternative arrangement of box and lid having a somewhat different configuration;

Figure 6 is a part cross-section of one side of a further alternative arrangement of box and lid having a somewhat different configuration;

Figure 7 is a schematic sectional side view of one embodiment of the second variation of the invention;

Figure 8 is a schematic cross-section taken along line of VII - VII in

Figure 7;

Figure 9 is a side view of a bottle having the alternative of a heat absorbent layer applied to its outer surface; and,

Figure 10 illustrates a flexible container having the general construction of an inflatable mattress. DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

In the embodiment of the invention illustrated in Figures 1 to 4 of the drawings, a solar water heater is generally indicated by numeral (1 ) and comprises a thermally insulated box (2) having a translucent lid (3) and a container in the form of a flexible, generally colourless, transparent plastic bag (4) for receiving water to be heated within the bag.

The thermally insulated box is made of a fluted, weather resistant sheet material that is, in this instance, a fluted extruded sheet of polypropylene material having multiple parallel elongate voids (6) that extend in the direction indicated by arrow "A". The voids are formed between parallel integral webs (7) of material extending between what are, in effect, two surface sheets (8) of the fluted sheet material, as shown clearly in Figure 4.

Such a fluted sheet of material may for example be that which is available internationally under the trade name CORREX ^R , and in South Africa under the trade name CORUPLAS™, a product marked by Ampaglass/Ampaplastics. This material is generally rigid and needs to be thermally treated along lines, or bent with a hydraulic press, where it is bent in order to form a box. For purposes of storage and transport, the boxes could either be made in a knockdown form for assembly by an ultimate distribution entity or by the consumer. As an alternative, they could be made to take a somewhat tapered shape from the top towards the bottom so that they can be nested for transport and storage purposes.

The voids in the type of material described above inherently provide a substantial degree of thermal insulation that may itself be sufficient for insulation purposes. Nevertheless, in this particular instance, a layer of additional thermal insulation is provided in the form of a heat insulating liner (9) that extends over all major surfaces of the inside of the box other than, of course, an open top. This additional thermal insulation may be of any suitable type and it is envisaged that a fibre reinforced reflective aluminium thermal insulation sheet such as that sold under the trade name SISALATION ^R by the South African Company AFRIPAK (PTY) LTD would be suitable.

A heat absorbing panel (1 1 ) is located between an inside surface of the heat insulating liner and the bag. The heat absorbing panel is made of a suitable heat absorbing plastics material selected to absorb radiant energy of radiation passing through the lid (see below) and bag and to transfer thermal energy thus absorbed by way of conduction or convection, or both, to the bag and its contents.

The bag is closed and has a single passage in the form of a tube (12) communicating with the interior thereof and passing through an aperture in a sidewall (13) of the box in order to serve as both an inlet and outlet to and from the interior of the bag. The passage has a closure (14) for opening and closing it.

The translucent lid (3) fits the open top of the box and is provided with a pair of parallel clear transparent sheets (16), such as of polycarbonate, spaced apart and that serve to thermally insulate the interior of the box whilst allowing solar radiation to pass through the lid and into the box. The two transparent sheets are, in the instance of the embodiment illustrated in Figures 1 to 3 of the drawings, held in spaced relationship by way of suitable transparent spacers (17) located between them. In this instance the peripheries of both of the sheets cooperate with the periphery of the top of the box.

The arrangement is such that, in use, water contained within the bag becomes heated by solar energy that passes through the translucent lid and the radiant energy that passes through the transparent bag and water therein strikes the heat absorbing panel to thereby become converted into thermal energy that can be transferred to the content of the bag by conduction or convection or both.

In order to assist in aligning the box with the midday sun at any particular time of the year, a tube (18) may be adhesively secured in one corner of the box so as to extend at right angles to the plane of the heat absorbing panel. The sun's rays (19) will, when the heat absorbing panel is at right angles to them, form an illuminated spot on the floor supporting the box. Setting up of the box in this manner should be carried out when the sun is directly overhead at any particular time of the year so that an advantageous amount of solar energy strikes the box and enters through the lid.

For use, the box may have one or preferably a pair of stays (21 ) associated with it for supporting an upper end region (22) of the box with the box in an inclined position, as illustrated in Figure 1 . Of course, any other support could be used for supporting the box at an incline. The box may thus be arranged to face into the sun in a generally North or South direction according to the location being in the Southern or Northern hemisphere and at an appropriate angle according to a time of year. The tube (18) described above may be used for this purpose. Alternatively, a graphic (23) may be provided on a side of the box, or on a label applied to the box, for indicating a preferred angle of inclination according to a time of year and degrees of latitude of the location at which the solar water heater is being used.

In use, the bag may be filled with water by way of the tube and the tube can be closed using the closure. The box is then orientated to face towards the North or South, as the case may be, and can be left over the day so that the water becomes hot. A user could, when returning from work for example, take the entire box indoors and use the hot water as required.

As shown in Figure 5, the edges of two spaced clear sheets (25) of plastic that form the lid could be located in spaced relationship relative to each other by means of a surrounding frame (26). Figure 5 also illustrates an alternative construction of the box in which panels (27) are cut and joined together by way of extrusions (28) along corners of the box with the edges of the joined panels being fitted, and as may be necessary, glued, into channels that receive the panel edges.

A still further alternative that is considered appropriate to low-cost manual fabrication, is illustrated in Figure 6. In this instance the side walls (51 ) and end walls (52) are each provided with pairs of spaced apertures (53) with the pairs themselves being spaced part along the length of the walls and inwardly of the free edge thereof in order to provide a series of pairs of spaced apertures around the periphery of the box. An inner clear plastic sheet (54) is supported inwards of the free edges of the side walls and end walls by means of cable ties (55) that are threaded through apertures in the clear plastic sheet and the apertures (53) through the walls so that a loop (56) of the cable tie is located on the outside of the box extending in a direction towards a free edge. The result is an inner clear plastic sheet supported inwardly of the periphery of the box.

An outer clear plastic sheet (57) is located over the open mouth of the box in the manner of a simple lid and a surrounding skirt (58) has slots (59) therein through which the loop (56) of the cable ties extends. A strap (61 ) may be threaded through the loops (56) of all of the cable ties on the outside of the skirt are so that the strap encircles the skirt (58) to hold the outer clear plastic sheet in position on the box.

Figure 6 also illustrates a cable tie (62) that is used to hold the edges of the end wall and side wall together so as to hold that the box in an erected condition. The use of cable ties in the manner described above is particularly convenient for manual erection and assembly of this particular embodiment of solar water heater according to the invention. It should be noted that one of the two transparent sheets (16, 25, 54) forming the lid may be omitted if an air gap can be effectively maintained between a single sheet and the bag. This can be done in any suitable way and one proposal is to use a construction in which the flexible bag has, as shown in Figure 9, portions thereof that form two opposite, generally parallel, major surfaces of the bag connected together at spaced positions (29) to limit their spacing when filled with water and thereby control the thickness of the filled bag in the manner of an inflatable mattress such as a lilo. The resultant thickness may be calculated to provide an air gap between the bag and what may be a single transparent sheet that forms the lid.

Turning now to the second variation of the invention, and with reference to Figures 6 and 7 of the drawings, one embodiment of the second variation provides for two juxtaposed parallel transparent bottles (31 ) each of which has a closure in the form of a screw cap (32). Each bottle may assume the form of a beverage or water bottle of a suitable size, typically a bottle having a capacity of from 1 .5 to 3 litres. The bottles are located parallel to each other in locating recesses (33) provided in a moulded foam insert (34) positioned within the box (35). The bottles may conveniently be made of a polyethylene terephthalate (PET) material as this material is commonly used at the present time for the production of beverage and water bottles. Of course, any other material can be used as on-going availability and technological development may indicate or dictate.

In this instance the lid (37) may have a single sheet (38) of transparent plastic material bent to an arched configuration with two end walls (39) holding the plastic material in this configuration. The end walls of the lid will typically fit inside the end walls of the box as shown clearly in Figure 6.

Figure 8 illustrates a further variation of the heat absorbing facility of the invention in that a bottle (41 ), in this instance, is provided with a heat absorbing layer (42) covering approximately one half of its outer surface so that the heat absorbing layer may be located innermost in its operative position. This may be used to avoid the necessity of having a separate heat absorbing panel, as described above. However, it does require a user to ensure that the layer is correctly orientated in the operative position. The same approach may be applied to a bag whether it be of a "NIo" type of construction or not.

Numerous variations may be made to the embodiments of the invention described above without departing from the scope hereof. In particular, the fluted sheet material may be a suitably weather resistant sheet of corrugated cardboard that would be more easily folded along fold lines in comparison to the fluted plastic material described above.