Tubular heating-pipe solar water-heating-system with integral tank
A collector core for a solar water-heating-system includes a plurality of heat-absorbing pipes each of which surrounds a cooler-water return-pipe. The heating-pipes may connect directly to an insulated hot-water storage-tank from which cooler water descends through the return-pipes into the heating-pipes. Upon reaching the end of the return-pipes, the cooler water flows outward into the space between the surrounding heating-pipes and the inner return-pipes. Upon warming, water between the two pipes rises upward back to the hot-water storage-tank thus completing the thermosyphon flow cycle. Preferably, the inner return-pipe is made of polyvinyl chloride (“PVC”), polybutelene (“PB”), or other compressible material which permits collector core operation both in freezing and non-freezing environments. Alternatively, the collector core may be added to an existing solar water-heating panel to improve its operation.
This application is an application for a patent of addition in respect of Australian Patent No. 702793, the contents of which are incorporated herein by reference.TECHNICAL FIELD
This invention relates generally to solar water-heating-systems, and more specifically to an improved solar water-heating-system having a collector core which includes heating-pipes in each of which countercurrent flows of hot and cold fluid pass in opposite directions.BACKGROUND ART
In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date:
- (i) part of common general knowledge; or
- (ii) known to be relevant to an attempt to solve any problem with which this specification is concerned.
A solar water-heating-system to which the present invention particularly relates comprises a solar water-heating-panel connected to a hot-water storage-tank. Such a solar water-heating-panel frequently includes vertically oriented, parallel heating-pipes or other channels embedded in a selective absorber, such as a black metal sheet, that is inclined towards the sun. The heating-pipes generally open into horizontal manifolds or header pipes both at the top and at the bottom of the solar water-heating-panel. Sunshine heats up the selective absorber and the pipes or other channels embedded in the selective absorber. This heat is transferred by conduction to a fluid, usually water, in the heating-pipes. Upon heating, the water expands slightly so its density becomes less than that of cooler water in the other parts of the solar water-heating-system. The hotter water then rises toward the top of the inclined panel and enters the horizontal upper manifold. The heated water then rises further from the upper manifold through a bend of one or two 90 degree elbow joints before entering the hot-water storage-tank. The new incoming hotter water upon entering the hot-water storage-tank pushes its way to the top, displacing cooler water already present in the hot-water storage-tank. The displaced cooler water first sinks to the bottom of the hot-water storage-tank, after which it continues to sink down a cooler-water return-pipe located at one side of the hot-water storage-tank and down the side of the solar water-heating-panel, makes another 90 degree turn in an elbow joint, to then enter the horizontal manifold at the bottom of the solar water-heating-panel. The cooler water, after entering the manifold at the bottom of the solar water-heating-panel, is heated again by the sun's rays and the process begins anew. Thus, the temperature of water in the hot-water storage-tank increases throughout the day.
Existing thermosyphon based solar water-heating-systems of this kind normally consist of a solar water-heating-panel with a separate insulated hot-water storage-tank placed immediately above the water-heating-panel. An example of a prior art of solar water-heating-system of this type is disclosed in U.S. Pat. No. 4,084,578 that issued Apr. 18, 1978, on an application filed by Toshihiro Ishibashi (“the Ishibashi patent”). A drawing depicting the solar water-heating-system disclosed in the Ishibashi patent is included herein as FIG. 0. The Ishibashi patent discloses increasing collection efficiency by improving the selective surface of the absorber through special paints and coatings, special non-reflecting glass, utilizing different corrugation profile angles for the collector sheet, and using the hot-water storage-tank as a reflector in winter.
Placement of the hot-water storage-tank in close proximity to and immediately above the solar water-heating-panel is known to be advantageous as disclosed in U.S. Pat. No. 4,766,885 that issued Aug. 30, 1988, on an application filed by Toshiaki Muramatsu (“the Muramatsu '885 patent”). However, in solar water-heating-systems such as that disclosed in the Muramatsu '885 patent, the hot water must flow horizontally across the breadth of the solar water-heating-panel, or even worse, across two panels if it is a two panel system, before entering the hot-water storage-tank. Moreover, before entering the hot-water storage-tank, the hot water must also flow through one or two elbow joints with all their attendant increase in resistance to flow due to form drag, i.e. eddying and turbulence, and friction drag etc. which impedes thermosyphon flow.
It is well known that slowing down natural thermosyphon flow reduces the efficiency of the heat collection because the water in the horizontal manifold becomes trapped, unable to move in its natural upwards direction. Consequently, water in the horizontal manifold gets hotter and hotter as it continues to absorb solar radiation. This relatively stagnant flow of hot water in the upper manifold, in the upper part of the heating-pipes, and in the elbow joints becomes disadvantageously hot, and radiates away heat through glass covering the solar water-heating-panel. Furthermore, some heat energy of the rising hot water in the vertical heating-pipes is also lost or expended in pushing the flow along the horizontal manifolds. All of these losses reduce the overall heat transfer coefficient of efficiency.
U.S. Pat. No. 4,353,352, that issued Oct. 12, 1982, to Michael F. Zinn (“the Zinn patent”), discloses an improved thermosyphon flow having a near direct connection from the heating-pipes to the hot-water storage-tank. However, solar water-heating-system disclosed in the Zinn patent forces the hot water to travel in a roundabout way from the top of the panel, curving behind the tank, before entering the tank itself. Furthermore, the Zinn patent also shows that upon entering the hot-water storage-tank the hot water must also flow downwards, against thermosyphon flow, because the outlets of the hot water inlet-pipes are located at the very top of the tank, pointing downwards. Placing the inlet-pipes at the top of the hot-water storage-tank causes hot water to build-up in this area and to become congested once some hot water has accumulated at the top of the tank. This congestion occurs because any new incoming hot water must drive the existing layer of hot water downwards within the hot-water storage-tank. Since this layer of hot water naturally resists flowing downward, the “plug” of hot water around the top of the tank effectively slows down the thermosyphon flow even more. Again, thermal collection inefficiency rises as the amount of hot water increases.
Known prior art solar water-heating-systems, including those disclosed in the Ishibashi and Zinn patents have the cooler-water return-pipe located at the side of the water-heating-panel. This location for the cooler-water return-pipe impedes the thermosyphon flow since horizontal runs, which impede the natural upwards or downwards movement of the thermosyphon flow, are then necessary across the width of the solar water-heating-panel(s). In prior art solar water-heating-systems, not only does the cooler water, which wants to sink, have to travel horizontally across the length of the hot-water storage-tank before finding the outlet leading down to the panel, but upon reaching the bottom of the panel, the cooler water must travel horizontally back across the width of the panel before reaching the furthest heating-pipe. Thus, in prior art thermosyphon solar water-heating-systems only a few of the heating-pipes near the lower manifold's inlet and the upper manifold's outlet operate at peak heat collecting efficiency. Consequently, a significant portion of a solar water-heating-panel located at a distance from the manifold's inlet and outlet experience stagnant or retarded flow.
U.S. Pat. No. 4,724,826, that issued Feb. 16, 1988, on another application filed by Toshiaki Muramatsu (“the Muramatsu '826 patent”), as well as the Muramatsu '885 patent, disclose a two phase system in which a working-fluid, gasified by solar radiation in an evaporator portion of a heat pipe, conducts heat to a condenser portion of the heat pipe where the working fluid returns to the liquid phase. In the solar water heaters disclosed in the Muramatsu '885 and '826 patents, gaseous heat-conducting fluid rises upwards while condensed heating-fluid descends downwards countercurrently within a multiplicity of hermetically sealed parallel channels included in a plate-like, solar heating-panel. In the systems disclosed in the Muramatsu '885 and '826 patents, the heating-fluid, apparently Freon or a like working fluid sealed within the plate-like heat absorber, must be isolated from the water to be heated in the hot-water storage-tank. Accordingly, in the systems disclosed in the Muramatsu '885 and '826 patents the water in the storage-tank is indirectly heated through conduction while passing through a heat exchanger which also contains the working-fluid, or an intermediate working-liquid heated by the gaseous first working-fluid.
Existing prior art solar hot water panels are also susceptible to mechanical damage if water in the heating-pipes freezes and cracks the heating-pipes. Some prior art systems have addressed this problem through an indirect system in which solar radiation heats an antifreeze solution in heating-pipes, or is heated at the condenser portion of heat pipes. The hot anti-freeze solution then circulates through a heat exchanger located in the hot-water storage-tank to heat the water. This type of solar water-heating-system is inefficient since the water is only indirectly heated by the antifreeze solution. Consequently, this indirect solar water-heating-panel system heats less water than a direct solar water-heating-system in which the water being heated circulates through heating-pipes. Moreover, indirect solar water-heating panel systems are more expensive and complicated that a direct solar water-heating-system, and require maintenance including regular topping up of any intermediate-working liquid antifreeze solution if such is used.SUMMARY OF THE INVENTION
Accordingly, one form of the present invention comprises an improved solar water-heating collector core adapted for incorporation into a solar water-heating-system by being joined to a lower portion of a hot-water storage-tank. The solar water-heating collector core comprises a plurality of hollow heating-pipes, each heating-pipe having a longitudinal axis and an interior that is surrounded by an outer wall. The heating-pipes, when assembled to form the collector core, are arranged so the longitudinal axes are disposed substantially parallel to each other with the heating-pipes inclined to the horizontal when in use with an upper end of each heating-pipe being elevated above a lower end. The lower end of each heating-pipes is closed, and the upper end of each heating-pipe is open and is adapted to extend directly to, open into, and communicate directly with a lower-level of the hot-water storage-tank, or with the lower portion of the solar water-heating-panel.
The solar water-heating collector core further comprises at least one cooler-water return-pipe enclosed within the outer wall of each heating-pipes. The cooler-water return-pipe within each heating-pipes has an internal cross-sectional area that is approximately equal to one-third (⅓) to one-half (½) of an internal cross-sectional area of the outer wall of the heating-pipes. Each cooler-water return-pipe has a length that is slightly longer than a length of the outer wall of the heating-pipes so the opening of the cooler-water return-pipe extends beyond the open upper end of the outer wall. Consequently, the upper end of the cooler-water return-pipe extends into and communicates directly with the lower level of the hot-water storage-tank, or with the lower portion of the solar water-heating-panel. The lower end of each cooler-water return-pipe is perforated so fluid may flow outward from within the lower end of each cooler-water return-pipe toward the surrounding outer wall of the heating-pipes.
In geographic regions that experience freezing temperatures, the cooler-water return-pipes are made of a compressible material for absorbing freezing pressure of ice formation during cold periods without damage to the collector core. The lower ends of the heating-pipes may be fitted with or without a drain valve or a cap and are free to move longitudinally to accommodate thermal expansion and contraction. Preferably, the middle portions of the heating-pipes are loosely secured to the solar water-heating-panel casing or frame by low friction sleeve collars with the lower ends of the heating-pipes loosely secured or seated on a spring or flexible corrugated polymer hose seat in a cup or sleeve collar fixed onto the solar water-heating-panel casing or frame.
In one embodiment of the present invention the heating-pipes are thermally joined to a heat-conducting sheet. An upper face of the heating-pipes and of the heat-conducting sheet has a heat-absorbing surface while a lower face of the heat-conducting sheet has a heat-reflective surface. In another embodiment of the present invention the heating-pipes are suspended slightly above a sheet having heat-reflective upper face and lower face. The sheet in this other embodiment is preferably corrugated parallel to the heating-pipes with the heating-pipes being located in the center of focus of the corrugations, and only the heating-pipes have a heat-absorbing surface.
In an alternative application of the invention the heating-pipes of the collector core extend into the bottom manifold of an existing solar water-heating-panel. Adding a collector core to an existing solar water-heating-panel boosts the heating capacity of the existing solar water-heating-system. The collector core also acts as a sediment trap which keeps the bottom manifold clean.
Because thermosyphon circulation is inherently weak and is susceptible to being slowed down by horizontal flows, or other impedances such as bends and elbows, eliminating such obstructions markedly improves heat collection efficiency. The advantage obtained by placing the outlet of the heating-pipes at the lower level of the hot-water storage-tank, pointing upwards as forms part of the present invention is not recognized in the Zinn patent where the hot-water inlet-pipes are at the very top of the hot-water storage-tank pointing downwards. The direct downward flow of cooler water from the lower level of the hot-water storage-tank through the cooler-water return-pipes to the lower end of the solar water-heating-panel also significantly improves collection efficiency.
These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.
The heating-pipes 108 are free to move longitudinally to accommodate thermal expansion and contraction. The middle portions of the heating-pipes 108 are loosely secured by low friction sleeve collars 234 to the solar water-heating-panel casing 148 or frame 232 with the lower ends of the heating-pipes loosely secured or seated on a spring 230 or flexible corrugated polymer hose seat 233 in a cup 231 fixed onto the casing 148 or frame 232.
The heating-pipes 108 are preferably spaced equidistantly apart as indicated in FIG. 1A.
In a highly preferred form, the heating-pipes 108 are spaced at approximately 90 mm centers, although this spacing may be varied to suit particular circumstances. The solar water-heating-panel 102 is preferably 945 cm wide, and excluding the hot-water storage-tank 104, is preferably 1750 cm long.
Each heating-pipe 108 has an outer wall 114, best illustrated in
As best illustrated in
As illustrated in
As best illustrated in
A portion of the solar water-heating-panel 102 extending below the casing 148 in the illustration of
The collector core 106 may be exposed, or part or all of it may be suitably housed within the casing 148 as in
As illustrated in
In either embodiment, when the heating-pipes 108 heat up, water between the outer wall 114 and the inner cooler-water return-pipe 116 rises into the hot-water storage-tank 104. Cooler water that has settled to the bottom of the hot-water storage-tank 104 is sucked into the cooler-water return-pipe 116 and flows downwards inside the cooler-water return-pipe 116 to replace the rising hot water. The cooler water then flows outward through the apertures 124 at the lower end 122 of the cooler-water return-pipe 116 toward the outer wall 114, and is heated in turn and starts to rise within the outer wall 114.
As can be seen particularly from
Although there is some minor conduction heat loss at night due to a close connection between the bottom of the hot-water storage-tank 104 and the heating-pipes 108, this heat loss is much reduced due to the stratification effect of the water in the hot-water storage-tank 104 acting as insulation layers. Only the water in the lower level 134 of the hot-water storage-tank 104 near the heating-pipe 108 cools down slightly, but this is more than made up by the improved collection efficiency during the day. Since the sheet 152, which forms the major surface area exposed to the glass, is not in direct thermal contact with the hot-water storage-tank 104 the heat loss is negligible. Placement of the collector core 106 below the hot-water storage-tank 104 also prevents reverse circulation at night when the panel radiates heat out into the night sky. Only the water inside the heating-pipe 108 is cooled by night time radiation, and since this cool water cannot descend any further, there is no reverse circulation when the sun is not shining. Thus at night, the hot water in the insulated hot-water storage-tank 104 remains hot and does not flow into the cooler collector core 106 below.
There is thus no horizontal flow at all in this solar collector core 106, leading to very high efficiencies in thermosyphon circulation. As the water becomes hotter and hotter towards the afternoon, the temperature differential between the top and bottom of the hot-water storage-tank becomes less and less. Similarly, the temperature differential between the hot water between the outer wall 114 of the heating-pipe 108 and cooler water in the cooler-water return-pipe 116 becomes less and less. If the cooler-water return-pipe 116 were laterally displaced as in prior art, i.e. at the side of the solar water-heating-panel 102, instead of directly inside the heating-pipes 108, the thermosyphon flow would slow down considerably in the afternoon due to the enforced horizontal flow and reduced temperature differential. The present invention does not suffer from this reduced flow in the afternoon as there is no horizontal flow. Accordingly, the thermosyphon flow occurs efficiently throughout the day.
Thermosyphon flow is not only inherently weak, but its natural movement is directly up or directly down, relying solely on the difference in densities between hot and relatively cooler water. Thus, any impediment to its free flow upwards or downwards such as enforced horizontal runs greatly reduces the overall efficiency of the solar heating system. As illustrated in
By reason of the present invention a considerable increase in the efficiency of thermosyphon flow can be obtained. The system allows hot-water 158 to flow upwards smoothly and directly without any inefficient twists or horizontal flow, and allows the return downward flow of cooler-water 159 to be similarly direct and with absolutely no horizontal flow component.
Placing the cooler-water return-pipe 116 inside the heating-pipe 108 also allows reducing the width of the solar water-heating-panel 102.
Cold water enters the hot-water storage-tank 104 from a supply tank or mains supply, not illustrated in any of the FIGS., preferably through a ball float valve 162 depicted in FIG. 1A. The ball float valve 162 preferably has a perforated outlet baffle 164 to prevent mixing of cold water with hot water. Hot water is drawn out at the top of the hot-water storage-tank 104 through a floating outlet 166 which ensures that the outlet is always at the topmost (hottest) level of the water in the hot-water storage-tank 104. The hot-water storage-tank 104, which includes an overflow 172, is enclosed within a housing 174 which can be formed from a metal, such as stainless steel or aluminium, or from a plastic material such a fiberglass. As illustrated in
The heating-pipes 108 may be secured to the hot-water storage-tank 104 or to the bottom manifold 192 of the collector core 106′ in various different ways. For example each heating-pipe 108 may be welded, coupled with compression fittings, clamped or glued to the hot-water storage-tank 104. Each heating-pipe 108 may also be similarly secured to the bottom manifold 192 of the collector core 106′ in these same ways, or may be screwed into a socket 212 provided by a coupling 214 as illustrated in FIG. 3B. The screwing of each heating-pipe 108 into the socket 212 in conjunction with use of the corrugations 144 and reflective surface 142 of the sheet 152, that are depicted in
The present invention preferably includes the cooler-water return-pipes 116 enclosed within the heating-pipes 108 to facilitate passage of countercurrent flows of rising hot-water 158 and descending cooler-water 159 without mixing or turbulence. However, if the cooler-water return-pipes 116 are removed from within the heating-pipes 108, thermosyphon flow still causes the hot-water 158 to rise up without interruption into the hot-water storage-tank 104, and the cooler-water 159 in the lower portion 193 of the hot-water storage-tank 104 to be sucked into the lower half of the heating-pipes 108. The cooler-water 159 sucked into the heating-pipes 108 then flows downward within the lower half of the heating-pipes 108 past the rising hot-water 158 which the cooler-water 159 replaces. Thus, in such a collector core 106 lacking the cooler-water return-pipes 116, the cooler-water 159 reaches the lower end 122 of the heating-pipes 108, is heated in turn, and then rises toward the hot-water storage-tank 104 in the upper half of the heating-pipes 108. This alternative embodiment collector core 106 lacking the cooler-water return-pipes 116 still avoids the horizontal flows that significantly impede thermosyphon flow, and that correspondingly reduce thermal collection efficiency.
While the invention has been described by way of a preferred embodiment in certain variations and modifications, other variations and modifications can also be used, the invention being defined by the following claims:
The word ‘comprising’ and forms of the word ‘comprising’ as used in this description and in the claims does not limit the invention claimed to exclude any variants or additions. Modifications and improvements to the invention will be readily apparent to those skilled in the art. Such modifications and improvements are intended to be within the scope of this invention.
1. A solar water-heating collector core adapted for incorporation into a solar water-heating-system either by being joined to a lower portion of a hot-water storage-tank, or by being joined to a lower portion of another solar water-heating-panel, the solar water-heating collector core comprising: wherein lower ends of the heating-pipes whether fitted with or without a drain valve are free to move longitudinally to accommodate thermal expansion and contraction.
- (a) a plurality of hollow heating-pipes, each heating-pipe having a longitudinal axis and an interior that is surrounded by an outer wall; said heating-pipes, when assembled to form the collector core, being arranged so the longitudinal axes are disposed substantially parallel to each other; said heating-pipes being adapted to be inclined to the horizontal when in use with an upper end of each heating-pipe being elevated above a lower end of each heating-pipe; the lower end of each heating-pipe being closed, and the upper end of each heating-pipe being open and adapted to extend directly to, open into, and communicate directly with a lower level of the hot-water storage-tank or with the lower portion of the solar water-heating-panel; and
- (b) a plurality of hollow cooler-water return-pipes, each of which is surrounded by the outer wall of one of the heating-pipes; the cooler-water return-pipe within each heating-pipe having an internal cross-sectional area that is approximately equal to one-third (⅓) to one-half (½) of an internal cross-sectional area of the outer wall of the heating-pipe, and having a length that is slightly longer than a length of the outer wall of the heating-pipe so the open upper end of the cooler-water return-pipe extends beyond the open upper end of the outer wall thereby permitting the upper end of the cooler-water return-pipe to extend into and communicate directly with the lower level of the hot-water storage-tank or with the lower portion of the solar water-heating-panel; and the lower end of each cooler-water return-pipe being perforated so fluid may flow outward from within the lower end of each cooler-water return-pipe toward the surrounding outer wall of said heating-pipe;
2. The solar water-heating collector core of claim 1 wherein middle portions of the heating-pipes are loosely secured by low friction sleeve collars to the solar water-heating-panel casing or frame and lower ends of the heating-pipes are loosely secured or seated on a spring or flexible corrugated polymer hose seat in a cup or sleeve collar fixed onto the solar water-heating-panel casing or frame.
3. The solar water-heating collector core of claim 2 wherein said heating-pipes are thermally joined to a heat-conducting sheet, wherein an upper face of said heat-conducting sheet and of said heating-pipes are provided with a heat-absorbing surface, and wherein a lower face of said heat-conducting sheet is provided with a heat-reflective surface.
4. The solar water-heating collector core according to claim 3 wherein said heating-pipes are disposed slightly above a sheet having heat-reflective upper face and lower face, and wherein said heating-pipes are provided with a heat-absorbing surface.
5. The solar water-heating collector core according to claim 4 wherein said collector core further comprises a casing having a transparent cover disposed over the heating-pipes, and thermal insulation disposed beneath the heating-pipes.
6. The solar water-heating collector core of according to claim 5 wherein the heating-pipes are adapted to screw into sockets that are joined either to the lower portion of the hot-water storage-tank, or to the lower portion of another solar water-heating-panel.
7. The solar water-heating collector core according to claim 6 wherein the heating-pipes are joined to the bottom manifold of the solar water-heating-panel.
8. The solar water-heating collector core according to claim 7 wherein said collector core further comprises the hot-water storage-tank.
9. The solar water-heating collector core according to claim 8 wherein said cooler-water return-pipes are made of a compressible material for absorbing freezing pressure of ice formation during cold periods without damage to the collector core.
International Classification: F24J 2/44 (20060101);