GB2079930A - Portable solar heaters - Google Patents

Abstract

A portable solar heater comprises a thermal insulating casing (10), e.g. moulded of high density foamed plastics material, with a transparent front cover (12), and housing a collector (14) in the form of an integrated absorber plate/tank unit. This unit comprises a tank (22) at the top, the tank having a top heated- water supply outlet (30), a front absorber plate (16), preferably of relatively thick aluminium, pipes (18, 20) for rising water immediately behind the absorber plate (16) and in intimate contact therewith. The riser pipes (18, 20) communicate with the bottom of the tank (22) at the front thereof, and a water return pipe (24) extends in spaced relationship to the absorber plate (16) between the bottom of the tank (22) at the rear thereof and a bottom junction (26) with the riser pipes (18, 20) whereat a cold water inlet (28) is located. The arrangement provides a thermo- siphon hydraulic circuit, while the location of the cold water inlet (28) at the lowest point of such circuit avoids disturbance of the hot water at the top of the collector (14). <IMAGE>

Description

SPECIFICATION Improvements in portable solar heaters Field of the Invention This invention relates in general to solar heating apparatus, and in particular to portable solar heaters.

Background to the Invention Portable solar heaters are intended for temporary connection to a cold water supply to enable a limited amount of heated water to be delivered instead of cold water in situations where other forms of heating for the water are unnecessary, undesirable, too expensive or simply not available. Examples of such situations are the provision of hot water for caravans, the heating of water for a garden paddling pool and the provision of heated water for a camp-site, as in a camp-site shower. It is an object of this invention to provide an improved portable solar heater which is convenient to transport and to use and has high heating efficiency.

The Invention According to the invention there is provided a portable solar heater which comprises a casing of insulating material having a transparent front cover behind which is located a collector in the form of an integrated absorber plate/tank unit which comprises a tank at the top, said tank having a top heated-water supply outlet, a front absorber plate, pipes for rising water immediately behind the absorber plate and in intimate contact therewith, said riser pipes communicating with the bottom of the tank at the front thereof, and a water return pipe extending in spaced relationship to the absorber plate between the bottom of the tank at the rear thereof and a bottom junction with the riser pipes whereat a cold water inlet is located.

The arrangement of the collector in accordance with the invention provides a true thermosyphon hydraulic circuit, while the location of the cold water inlet at the lowest point of such circuit avoids disturbance of the hot water at the top of the collector.

Further Features of the Invention Preferably the collector has two riser pipes at the front, said two riser pipes forming a U-shape the limbs of which are relatively widely spaced across the absorber plate in symmetrical relationship to the lateral centre thereof, e.g.

spaced by half the overall width of the absorber plate which forms the front of said collector. A single return pipe at the rear of the collector may then be located in line with the lateral centre of the absorber plate. The use of a relatively thick absorber plate, preferably of aluminium, to which box section riser pipes are soldered or otherwise intimately secured, enables the number of riser pipes to be minimised at two without impairing the efficiency of overall thermal energy transfer from the absorber plate to the water in the riser tubes. The preferred arrangement of two front riser pipes at relatively wide centres with a rear central return pipe promotes relatively rapid thermosyphonic circulation within the collector to achieve a store of heated water in the tank in a relatively short time.

Preferably, the casing is a one piece, high density plastics foam, moulded box with a transparent plastics, e.g. acrylic, cover providing both mechanical enclosure and a high degree of thermal insulation which enables the water to be heated to and maintained at high temperatures.

A still further feature of the apparatus resides in the provision of a folding rear stand, which can be located in a first position to serve as a carrying handle for the heater and in a second position to serve as a stay which will support the heater on the ground at an optimum operative inclination.

In the Accompanying Drawings:- Figure 1 is a front view of a portable solar heater in accordance with the invention; Figure 2 is a transverse cross-section through the heater when supported on the ground ready for use; Figure 3 shows, to an enlarged scale, a detail of the pipe junction at the bottom of the collector; and Figure 4 diagrammatically illustrates an alternative manner of mounting the heater ready for use.

Description of Embodiment Referring to Figures 1 and 2, the heater has a thermal insulating casing 10 moulded of high density foamed plastics material, with a transparent cover 12 of acrylic plastics or other suitable material.

With the casing 10 is a collector, generally designated 14, which includes a front absorber plate 16, conveniently of aluminium for good thermal conductivity coupled with long life. This plate 1 6 is relatively thick, for example being formed of aluminium 1 8G.NS3 sheet. To the rear of the absorber plate 1 6 are soldered two boxsection riser pipes 18, 20 (see Figure 1), say of 1 9 mm times 1 9 mm internal cross-sectional dimensions, which together define a U-shape with limbs at relatively wide centres. At the top, the riser pipes 18, 20 enter the bottom of a full width hot water storage tank 22, at the front of said tank adjacent the upper edge of the front absorber plate 1 6.From the rear centre of the bottom of the tank 22, a return pipe 24, say of 19 mm x 38 mm internal cross-sectional dimensions, leads to a bottom junction 26 with the riser pipes 18, 20, i.e.

at the bottom of the U. The pipes 1 8, 20 and 24 may be formed of steel or other suitable metal or alloy, such as 1 6G-HE9 box section.

The junction 26 is shown in the detail of Figure 3, which also shows a cold water inlet 28.

13 mm outside diameter round section, communicating with said junction. A hot-water supply outlet from the top of the tank 22 is indicated at 30 in Figures 1 and 2.

The absorber plate 16, pipes 18, 20, 24 and tank 22, together with the cold inlet 28 and a hot outlet 30, constitute a collector 14 manufactured as an integrated absorber plate/tank unit. This unit 14 is inserted into and located within the moulded insulating casing 10, or alternatively the casing 10 may be moulded around the unit 14. The cover 12 is then fixed over the front of the absorber plate 1 6, conveniently by means of a locating slot 32 in the top wall of the casing and fixing screws 34 near the bottom of the casing.

In use, a true thermosyphonic circulation is produced within the heater as water rises through the riser pipes 18, 20 and falls through the return pipe 24. Hot water in the tank 22 is substantially undisturbed by the remote entry of cold water at the lowest point of the circuit, i.e. bottom junction 26.

The complete collector unit is sized to give a specific ratio of volume to surface area, conveniently about 9.7 litres/m2. With the described circulatory arrangement of the collector and the good insulation provided, this ensures that a relatively small quantity of water is heated rapidly to a good working temperature, which is important for caravan and camp-site use. Tests have shown that the contents of the heater will rise from about 600F to 1 200F in about 30 minutes in bright sunshine, and that the unit will eventually boil in about 12 hours.

Figure 2 also shows how the heater can be supported on the ground, at an optimum operative inclination for use, by means of a rear stand 40.

This stand 40 is pivotally mounted to the top of the casing 10 by means of a hinge 42, so that it can be folded from the position shown in the drawing, towards the back of the heater, into a second position in which its upper end portion 44 can serve as a carrying handle. The heater is relatively dimensioned so that, when carried by the folded back stand 40 serving as a handle, a comfortable hold is afforded to an average person without risk of the heater hitting the ground.

Figure 4 shows an alternative mode of use of the heater, attached to the sill of a caravan window by means of a hook 50, for example formed integrally with the handle portion of the stand 40, with a supplementary stay 52 provided to hold the heater at the correct inclination.

Various modifications of the above-described embodiment are possible within the scope of the invention. For example, the riser and return pipes within the collector may be differently arranged while preserving the thermosyphonic circulation through the bottom of the integrated top tank.

Different materials may also be employed, compatible with the preferred use of an aluminium absorber plate.

Claims (12)

1. A portable solar heater comprising a casing of insulating material having a transparentfront cover behind which is located a collector in the form of an integrated absorber plate/tank unit which comprises a tank at the top, said tank having a top heated-water supply outlet, a front absorber plate, pipes for rising water immediately behind the absorber plate and in intimate contact therewith, said riser pipes communicating with the bottom of the tank at the front thereof, and a water return pipe extending in spaced relationship to the absorber plate between the bottom of the tank at the rear thereof and a bottom junction with the riser pipes whereat a cold water inlet is located.

2. A portable solar heater according to claim 1, wherein the collector has two riser pipes at the front, said two riser pipes forming a U-shape the limbs of which are relatively widely spaced across the absorber plate in symmetrical relationship to the lateral centre thereof.

3. A portable solar heater according to claim 2, wherein the two riser pipes are spaced by half the overall width of the absorber plate which forms the front of said collector.

4. A portable solar heater according to claim 2 or 3, wherein a single return pipe at the rearof the collector dislocated in line with the lateral centre of the absorber plate.

5. A portable solar heater according to any one of the preceding claims, wherein the absorber plate is relatively thick.

6. A portable solar heater according to any one of the preceding claims, wherein the absorber plate is of aluminium.

7. A portable solar heater according to any one of the preceding claims, wherein box section riser pipes are soldered to the absorber plate.

8. A portable solar heater according to any one of the preceding claims, wherein the casing is one piece, high density plastics foam, moulded box.

9. A portable solar heater according to any one of the preceding claims, wherein the cover comprises transparent plastics material.

10. A portable solar heater according to claim 9, wherein the cover is of acrylic plastics material.

11. A portable solar heater according to any one of the preceding claims, further comprising a folding rear stand, which can be located in a first position to serve as a carrying handle for the heater and in a second position to serve as a stay which will support the heater on the ground at an optimum operative inclination.

12. A portable solar heater substantially as herein described with reference to, and as shown in, the accompanying drawings.