[0001] This invention relates to a solar heating system.

[0002] A typical solar heating system either includes a flat plate collector, or an evacuated tube collector, although other configurations do exist. [0003] The flat plate collector consists of a solar panel which is connected to a storage tank or geyser that is usually positioned above the solar panel or inside a roof space between a roof and a ceiling. The flat plate collector utilizes the thermosiphon principle wherein cold water flows into a bottom of the solar panel. The panel is heated by the sun and this causes hot water to rise up to the storage tank or geyser. Albeit being the most commonly used solar heating system, cost effective and relatively easy to manufacture, the system can fail when exposed to temperatures below freezing point. It has also been found that the panel may block with sediment and stop functioning.

[0004]An evacuated tube collector includes a plurality of cylindrical glass tubes that are attached to a frame which is positioned on the roof. Each tube includes a copper rod extending from the bottom of a frame to a top of the frame and then into a manifold. Each tube contains a liquid chemical formulation which boils at a predetermined temperature. The resulting vapour or gas heats the copper rod inside the tube and the rod in turn heats the water in the manifold. The manifold is connected to a storage tank or geyser. This system is laborious to assemble and the tubes are susceptible to the elements. It has been found that this system may stagnate if not used regularly. [0005] US patent number 4,505,261 , “Modular Passive Solar Heating System”, describes an arrangement which includes a plurality of heat tubes which are arranged to form a flat plate solar collector and which are connected to a storage tank or geyser via double-walled heat exchangers that penetrate the storage tank to enhance heat transfer. Solar radiation heats the flat plate collector which then heats a fluid inside the tubes. The fluid evaporates and gas rises inside each tube to the heat exchanger. This causes heat to be transferred to water in the storage tank. The gas condenses to a liquid phase which returns to lower sections of the tubes.

[0006] The mounting of the heat exchangers to the storage tank in a leak proof manner is an exacting technical task which adds materially to the cost of the storage tank.

[0007] An object of the current invention is to produce a solar heating system which is robust and resistant to freezing and stagnation, and which can be manufactured with relative ease.

SUMMARY OF INVENTION [0008] The invention provides a solar heating system for use with a storage tank, the system comprising a first manifold, a second manifold which includes an inner tube and an outer tube, a jacket which is formed between opposed surfaces of the inner tube and the outer tube and which is connectable to the storage tank, a plurality of riser tubes which extend between the first manifold and the second manifold, and which in use are inclined upwardly to the second manifold, and a fluid within at least the first manifold, wherein the fluid when heated by solar radiation evaporates and releases vapour into the tubes, which vapour condenses in the jacket to transfer heat energy into the inner tube. [0009] The first manifold may be configured to be a common reservoir for the riser tubes, and the jacket in the second manifold may be configured to be a common condenser for the riser tubes.

[0010] Heated fluid may be transferred from the inner tube to the storage tank via a pump or via the thermosiphon principle.

[0011] The first manifold, the tubes, and the second manifold may comprise a sealed system.

[0012] A vacuum may be drawn from the system before the system is sealed. The vacuum may be in the range of 1 - 29.9 in Hg. Preferably, the vacuum is of the order of 25 in Hg. [0013]The reduction in pressure decreases the boiling point of the fluid.

[0014] The fluid formed by condensation of the vapour at the jacket may return under gravity action to the first manifold. The aforementioned process is repeated continuously.

[0015] The solar heating system may include a drain for ensuring that fluid in the jacket returns to the first manifold. Preferably a respective drain is positioned at each end of the outer tube, to return fluid to an adjacent riser tube.

[0016] The volume of the fluid in the sealed system may vary and may be in the range of 1-99% of the capacity of the system. Preferably, the volume is of the order of 75% of the capacity of the system.

[0017] The outer tube in the second manifold may have a larger diameter than the diameter of each of the riser tubes. [0018] The riser tubes and the manifolds may be located inside a sealed volume.

[0019] A transparent cover may overlie the sealed volume.

[0020] A sheet of solar collector material may be positioned inside the volume. The riser tubes may be mounted in heat-transferring contact with a surface of the solar collector material.

[0021] The fluid may be any appropriate liquid (e.g. water or a specially formulated composition) or gas.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention is further described by way of examples with reference to the accompanying drawings in which:

Figure 1 is a plan view of a plurality of riser tubes and manifolds which form a part of a solar heating system according to the invention,

Figure 2 is a side view on an enlarged scale of an upper part of the solar heating system, Figure 3 is a partly sectioned side view of the solar heating system, Figure 4 is a schematic illustration of the solar heating system in use, and

Figure 5 illustrates a variation of the riser tubes shown in Figure 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0023] Figure 1 of the accompanying drawings is a plan view of components of a solar heating system 10 according to the invention - see Figure 3 as well. [0024] The solar heating system 10 includes a first manifold 12 and a second manifold 14. The second manifold 14 includes an inner tube 16 and an outer tube 18. An annular jacket 20 is formed between an outer surface of the inner tube 16 and an opposed inner surface of the outer tube 18 - see Figure 2 which is a side view in section on an enlarged scale of an upper part of the solar heating system 10.

[0025]A plurality of metallic riser tubes 22, preferably of copper, extend between the first manifold 12, which forms a common reservoir for the tubes 22, and the second manifold 14. The jacket 20 forms a common condenser for the tubes 22.

[0026] The first manifold 12, the tubes 22, and the second manifold 14 collectively create a sealed system 26.

[0027] A vacuum is drawn before the system is sealed. Preferably, the vacuum is of the order of 25 in Hg.

[0028] A fluid, preferably water 28, is inside the sealed system 26. The vacuum is drawn by using any suitable valve, such as a Schrader valve, before the water 28 is placed inside the sealed system 26. The vacuum provides insulation against conduction, convection, and radiation.

[0029] The volume of the water 28 inside the system 26 varies according to requirement and, in one form of the invention, is equal to about 75% of the volume (capacity) of the sealed system 26. [0030] Figure 3 is a partly sectioned side view of the solar heating system 10, in use. The components shown in Figure 1 are located inside a support frame 36. The frame 36 includes a surround 38, an insulating support base 40 and an overlying transparent cover 42 made for example from toughened glass. The components shown in Figure 1 are fixed to the support base 40 so that the first manifold 12 is lowermost, the second manifold 14 is uppermost and the riser tubes 22 are inclined at an optimum angle to incident solar radiation 46 at an installation site. The tubes 22 are located below and are in heat transferring contact with a metallic solar collector plate 48 which is covered with a material which enhances its capability to absorb heat from the solar radiation 46. The components shown in Figure 1 are fixed to the support base 40 by means of a conductive adhesive or by laser or ultrasonic welding. [0031] The outermost tubes, 22A and 22B respectively, include drainage tubes 50

(notionally shown in Figure 1 ) which are connected in parallel to the jacket 20. This is better shown in Figure 2 which illustrates an upper end of the tube 22B which is in fluid communication with the jacket 20 and which is in parallel with the drainage tube 50 which is connected to the jacket 20 and to a port 52 in a wall of the tube 22B, a short distance from the jacket 20.

[0032] The inner tube 16 is connected at one end by means of insulated piping 80 to a lower inlet 82 of a storage tank or geyser 84 - shown in Figure 4. Water 86 flows from the lower inlet 82 through the storage tank 84 to an upper outlet 88 and returns via an insulated pipe 90 to an opposing end of the inner tube 16 via the thermo-siphoning principle. [0033] In use of the system, solar radiation 46 which impinges on the collector plate 48 heats the underlying tubes 22 and heat energy is transferred to the tubes 22 by conduction. [0034] The water 28 in the lower manifold 12 is caused to boil and creates steam, which rises in the tubes 22 to the jacket 20 in the second manifold 14. The steam contacts the outer surface of the inner tube 16 which contains relatively cold water 86. The steam then condenses inside the jacket 20 and heat energy is transferred to the water 86. As stated, the heated water in the jacket then rises via the pipe 80 to the storage tank 84 and is replaced by cooler water which flows from the tank via the pipe 90. This process continuously proceeds.

[0035] The reduced pressure in the sealed system 26 decreases the boiling point of the water 28 which then evaporates at a lower temperature. [0036] The solar heating system 10 is customizable to suit specific regions e.g. freezing conditions.

[0037] The solar heating system 10 is aesthetically pleasing, robust, and is resistant to hail, freeze and stagnation. It is cost effective to manufacture.

[0038] In freezing conditions the water 28 will remain in the condensed state before returning to the first manifold 12. The vacuum between the inner tube 16 and the outer tube 18 i.e. in the jacket 20, provides insulation which prevents the cold from radiating or conducting onto the inner tube 16 - this helps to prevent freezing of the water 86 in the inner tube 16.

[0039] Any suitable fill or heat transferring medium (gas or liquid) can be used within the sealed system 26 but as described hereinbefore, water is preferable. [0040] Preferably the solar heating system 10 is of the following order: the first manifold 12 is 15mm in diameter, the inner tube 16 is 22mm and the outer tube 18 is 32mm in diameter, each riser / tube 22 is 10mm in diameter, each drainage tube 50 is 10mm in diameter, the insulating support base 40 is 20mm thick, the overlying transparent cover 42 is 4mm in diameter, and there is a 20mm air gap between the tubes 22 and the collector plate 48.

These dimensions have been established by trial and experiment to give excellent results but, nonetheless, are exemplary only.

[0041] Figure 5 shows a variation of the invention wherein each of tubes 22 (which are of circular form) is replaced by a tube 22X which has a flattened surface 96 which is in heat- transferring contact with the collector plate 48.

[0042] The flattened surface 96 provides a larger area for receiving heat via conduction from solar radiation 46 impinging on the collector plate 48 to heat the underlying tubes

22X.