MULTI-LAYER THIN FILM SOLAR COLLECTOR
A solar collector is provided that is formed from relatively thin polymer sheets. Three or more sheets are welded together to integrally define a storage tank, a plurality of layers of fluid flow channels (e.g. risers), and other desired features within the collector. The storage tank is located at a first end of the collector and a heat exchanger is provided within the storage tank. The heat exchanger is arranged to transfer heat from the storage tank to a target fluid (such as water) that is to be heated or preheated by the collector. The collector is arranged so that when it is installed, the collector may be positioned with the storage tank located generally above the fluid flow channels. The storage tank and the fluid flow channels are arranged such that when the collector is installed and filled with a working fluid, a thermosiphon effect will cause the collection of hot water within the storage tank.
The present invention relates generally to solar heat collection panels. More particularly, the invention relates to thin film solar collectors.
Solar heat collection panels have been used for a number of years to heat or preheat water and/or other fluids for a number of applications. Many collectors utilize a metal collection plate having a number of metal riser tubes or tubes with fins that extend between header pipes (often called manifolds). Often, the collection plates are housed within an insulated box with a transparent glazing placed over the front surface of the collector panel.
Another type of solar heat collection panel contemplates eliminating the collection plate and rather simply runs a series of side-by-side riser tubes between a pair of header pipes. The header pipes and risers can be formed from a wide variety of materials, but one class of heat exchangers use simple extruded plastic or elastomer tubing. When plastic tubing is used as the risers, adjacent tubes can be extruded, tack welded or supported together so that an array of side-by-side tubes forms a collection panel. A variety of plastics may be used to form the panels, although generally a dark, thermoplastic material is used. Such panels have been sold for a number of years by FAFCO Inc. of Chico, Calif., and are described, for example, in U.S. Pat. No. 4,205,662.
Although these and other existing solar panel designs work quite well, there are continuing efforts to develop new collector designs that not only meet the needs of specific applications but also are also stronger and more reliable.
U.S. Pat. No. 4,143,644 describes a solar panel design that is formed by welding two plastic sheets together. Although the patent describes a low cost collector design, the design does not appear to have enjoyed substantial commercial success. It is believed that one of the reasons for this is that the described design appears to be highly susceptible to: (a) stress concentrations that can lead to collector failures at the transition between riser tubes and the bottom manifold; and (b) non-uniform thermosiphon fluid flow in the riser tubes since upward and replacement flow occur in the same layer.
SUMMARY OF THE INVENTIONIn accordance with an embodiment, a solar collector is provided. The solar collector includes a front sheet formed from a polymer film, a middle sheet formed from a polymer film, and a back sheet formed from a polymer film. The front, middle, and back sheets are welded together, with the middle sheet between the front and back sheets, to define a storage tank, a manifold and two layers of fluid flow channels. Each layer of fluid flow channels includes a plurality of fluid flow channels that extend substantially longitudinally between the manifold and the storage tank. Each of the fluid flow channels opens directly into the storage tank, and the storage tank is located at a first end of the collector and the manifold is located at a second end of the collector.
In accordance with another embodiment, a solar collector is provided. The solar collector includes a front sheet formed from a polymer film, a middle sheet formed from a polymer film, and a back sheet formed from a polymer film. The front, middle, and back sheets are welded together, with the middle sheet being between the front and back sheets, to form a first layer of fluid flow channels between the front and middle sheets and a second layer of fluid flow channels between the middle and back sheets. Each layer of fluid flow channels includes a plurality of fluid flow channels that extend substantially longitudinally along the solar collector.
In accordance with yet another embodiment, a solar collector is provided. The solar collector includes a front sheet formed from a polymer film, a middle sheet formed from a polymer film, and a back sheet formed from a polymer film. The back sheet has substantially the same length as the front sheet and the middle sheet is shorter than the front and back sheets. The front, middle and back sheets are welded together to define first and second layers of substantially parallel fluid flow channels that extend longitudinally along the collector. The first layer is between the front sheet and the middle sheet and the second layer is between the middle sheet and the back sheet.
The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:
It is to be understood that, in the drawings, like reference numerals designate like structural elements. Also, it is understood that the depictions in the figures are diagrammatic and not to scale.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTSThe present invention relates generally to solar heat collection panels formed from relatively thin film sheets.
Referring initially to
In the context of this description, the terms “top”, “bottom”, “front”, “back” and “vertical” are used primarily in the context of describing the drawings. It should be appreciated that when the solar collectors are installed, the storage tank would typically be positioned above the riser portions of the collector, although the collector would typically not be mounted vertically. Rather, it would be installed at an angle that is appropriate for the location at which the collectors are installed.
In the illustrated embodiment, the welds are arranged to define a closed collector having an integrally formed storage tank 23 and two layers, each having a multiplicity of adjacent riser type fluid channels 26.
As shown in the embodiment illustrated in
As shown in
As shown in
In the illustrated embodiment, with three polymer sheets 60, 62, 64, the solar collector 20 has two layers 70, 72 of risers or fluid channels 26. There is a front layer 70 of risers 26 between the front sheet 60 and the middle sheet 62, and there is a back layer 72 of risers 26 between the back sheet 64 and the middle sheet 62. As shown in
In the embodiment illustrated in
In the context of the collector 20, a storage tank 23 is positioned on the “top” side of the collector 20 and the riser welds 32 extend “vertically” downward below the storage tank 23. In order to form the integral storage tank 23, the middle sheet 62 is shorter than the front and back sheets 60, 64.
Also, in this embodiment at the bottom of the collector 20, the middle sheet 62 does not extend all the way to the bottom peripheral weld 29. With this arrangement, a manifold 38 is effectively formed at the bottom end of the collector body so that a working fluid within the collector body can flow between hot and cold paths within a riser 26, as shown in
Alternatively, in another embodiment, the middle sheet 62 can extend all the way to the bottom peripheral weld 29 and holes and/or a mesh strip can be provided in the middle sheet 62 near the bottom to allow flow of the working fluid between layers 70, 72. The riser welds 32 extend all of the way to the peripheral collector body weld 29 at the “bottom” of the collector 20 so that adjacent risers 26 in the same layer are separated from one another. As shown in
As discussed above, in the embodiment shown in
The solar collector 20 also has at least one fill and drain port 35 that permits the collector 20 to be filled with (and drained of) a suitable working fluid, such as water or an antifreeze solution (e.g., brine or a glycol type solution). In the embodiment illustrated in
In the embodiments shown, the fill and drain port 35 and the air port 44 are formed by simply defining a fill channel and an air channel in the collector body that is open to the outside of the collector body. The collector 20 can then be filled by inserting a hose, a funnel, or other suitable fluid supply source into the fill channel Any air that gets trapped within the collector during filling may be released through the air port 44 before, during or after the collector is filled. After the collector has been filled, the air and fill ports may be closed by a valve, or by folding over and clipping a tube to form a water-tight seal. Alternatively, an air bleed valve can be used.
In still other embodiments, a plastic fitting or other appropriate connector may be welded to, clamped or otherwise attached to the fill port (e.g., using a hose clamp). A removable (e.g. threaded) cap, valve or plug can then be secured to the fitting to seal the fill port. Embodiments of suitable fill and drain ports are described below with reference to
In the illustrated embodiment, as shown in
In some embodiments, the tie down channels may extend the entire width of the collector panel. This type of arrangement may be particularly appropriate in situations where no ports are provided along the edge with which the tie down channel is aligned. In other instances, the tie down channels may extend only a portion of the width of the collector panel, or may be segmented. In the embodiment shown in
In some embodiments, the heat exchanger can be positioned in the storage tank 23. In the embodiment shown in
In another embodiment shown in
Referring next to
It should be appreciated that although a particular water preheating system is described, the described collectors may be used in a very wide variety of different systems. For example, they may be used as the sole source of hot water, in pool heating applications, as water heaters for radiant space heating applications, etc. Of course, any suitable number of solar collectors 20 may be used within the solar collection system. In some arrangements, it may be desirable to plumb multiple collectors together in series, whereas in other applications it may be desirable to plumb multiple collectors together in parallel or in other arrangements.
It should be apparent that the described collectors do not have any internal pumps or other moving parts that are arranged to circulate the fluid within the collector. Thus, the working fluid within the collector is not pressurized (although it will typically be desirable to pressurize the external water that passes through the heat exchanger). Thus, the collector works as a thermosiphon system.
With three or more layers of thin film sheets, flow paths can be separated. For example, a front layer 70 of channels or risers 26 is provided for hot water thermosiphon flow and a back layer 72 of channels or risers 26, which is separated from the front layer 70, is provided for downward flow of cold water, as shown in
Since the collectors 20 are made from thin film materials, the collector 20 will effectively inflate when filled with a working fluid (e.g., water or an antifreeze solution).
Generally, any size sheets may be used. By way of example, widths on the order of 1½ to 10 feet (more preferably about 4 feet) and heights on the order of 4-14 feet (more preferably 12 feet) are believed to be appropriate for most applications. The widths of the risers may also be widely varied. By way of example, unfilled riser widths of ¼ to 6 inches (more preferably ½ to 1½ inches) are believed to be appropriate for most applications. The dimensions of the storage tank can also be widely varied. By way of example, in the embodiments shown in
The described collectors are extremely inexpensive to produce. The collection efficiency of the described collectors is less than most conventional solar collector designs. However, they have a calculated solar fraction (SF) of about 50-65% in sun belt locations for a collector area of about 60 square feet. The design philosophy was to produce solar heat at relatively low efficiencies, but at a very low installed cost while minimizing stagnation and freezing risks.
As discussed above, the described arrangement is a passive collector that has a thermosiphonic flow. Common thermosiphon designs have a designated flow channel for carrying fluid to the tank, and a separate one for carrying fluid to the bottom collector manifold. Experiments have demonstrated that with the described arrangement, at any given time, the risers 26 in one layer 70 carry the working fluid upward, while the risers 26 in the other layer 72 carry the working fluid downward, as shown in
The collectors can be unglazed, as illustrated in
The heat exchanger 50 may take a wide variety of forms. Preferably, the heat exchanger is a self-contained unit that may be sealed inside the storage tank and plumbed to the heat exchanger ports 52. Representative heat exchanger units 50 are illustrated in
A polymer heat exchanger 50 can be used with the collector 20. The heat exchanger 50 includes a multiplicity of plastic tubes having a pair of manifolds on opposing ends. In an embodiment, a threaded portion of the manifold can be screwed into the heat exchanger port 52 to form an appropriate seal on both ends of the heat exchanger 50.
The diameter and length of the tubes may be widely varied to meet the needs of any particular application. Preferably, the tubes will have small diameters and relatively thin walls. By way of example, polymer tubes having an outer diameter in the range of approximately 0.08 to 0.25 inches work well for many applications, although both larger and smaller tube diameters may be used in particular applications. Inner tube diameters may also vary widely although it should be appreciated that thin walls are generally preferred since thin walls will generally improve the heat exchangers thermal performance by decreasing the temperature drop across the tube walls. In a preferred configuration the tubes are separated from each other and bent into a serpentine configuration.
The manifolds may take a variety of geometries and are preferably configured to facilitate coupling to fluid supply and drain conduits.
The tubes and manifolds may be formed from a wide variety of plastics and other polymers. By way of example, Polyethylene, Polypropylene, Polyamide, Polysulfone, and Polyphenylene Sulfide work well for both the tubes and the manifolds. Of course, in other embodiments, a wide variety of other plastics and polymers may be used. The tubes and manifolds may be formed from the same materials, substantially the same materials or different materials depending on the requirements of any particular application.
Of course, in alternative embodiments, a variety of other heat exchanger designs can be used. In some embodiments, the heat exchanger may be provided with end caps that mate with the heat exchanger ports 52. The end cap design would vary based on the design of the corresponding heat exchanger port. The fill and drain port 35 may also be configured in a variety of manners.
In the initially described embodiment, the collector 20 is formed by welding three sheets of plastic together in a manner that defines the storage tank 23, two layers of side-by-side risers 26, ports and other components. It should be appreciated that in practice, the three sheets that are welded together may be formed from three or more separate rolls of film material. Those familiar with thin film sheet production will know that films of this type are sometimes formed in a tubular manner and an extended length of the film is provided on a roll.
A variety of different materials can be used to form the collector. Preferably, the material is one that resists degradation and otherwise holds up well under direct exposure to sunlight. By way of example, 6 mil thick black polypropylene or polyethylene work well. Of course the thickness of the material can be widely varied.
One feature of the described collector arrangement is that the outer layers can be thicker than the middle film layer, which will pillow out less when filled.
One of the significant advantages of the described thin film collector is that the geometry of the collector, the flowpaths within the collector, the size, number and geometry of the storage tanks, risers, manifolds, ports and the other components may be widely varied to meet the needs of a particular application with minimal effort (i.e., simply by setting up the welds appropriately for a desired new design).
Referring next to
The water enters the collector through an inlet 442 and exits through an outlet 444. The position of the inlet and outlet may be widely varied, although generally it is preferable to have the inlet at or near the bottom and the outlet at the top of the collector.
It is well understood in the thermal solar collection arts that glazing can be used to improve the thermal efficiency of a collector. Thus, in an embodiment, a thin film glazing layer 61 can be provided on a solar collector, as shown in
With the described arrangement, the stagnation temperature of the collector can be controlled somewhat by adjusting the amount of air (which acts as an insulator) within the air pockets. If the glazing is completely deflated, then the stagnation temperature of the collector under any given operating condition will be reduced compared to a state in which the air pocket are fully inflated. This feature makes it possible to control the stagnation temperature of the collector somewhat by controlling the level to which the glazing is inflated.
It should be appreciated that the glazing effectively insulates the top surface of the collector. In alternative embodiments, a similar air gap type insulation layer can be provided over other surfaces of the collector. By way of example, a thin film insulating layer similar to the glazing layer can be attached to the bottom surface of the back collector sheet 64 in a similar manner. When the region between the insulating layer and the back collector sheet is filled with air, it serves as an insulator for the bottom surface of the collector. Of course, if the insulating layer is not itself exposed to sunlight, there is no need for it to be transparent or translucent. Similarly, air gap type insulating layers can be provided over any or all surfaces of the storage tank, or polymer foam 65 can be welded to the back collector sheet 64, as shown in
The described thin film collectors are very versatile and can be used in a wide variety of applications. In the primary described embodiments, the collector is a passive device that does not have any pumps or the like. The water (or other working fluid) within the collector circulates due to thermosiphonic flow. The heat exchanger receives pressurized water (as for example city water), which is heated within the storage tank and fed to the desired location (e.g., to a hot water heater, to an appropriate tap, etc.).
Thin film collectors can also be used in active systems, with or without a heat exchanger, in which some mechanism would be needed to circulate the water to be heated. For example, a pump could circulate fluid through the internal heat exchanger in the film collector to heat fluid in an external storage tank. Alternatively, if the collector is used without an internal heat exchanger, water may be pumped through the collector and then fed directly into the system in which it will be used. In one example, if the water entering the collector is pressurized (e.g. city water) a float value could be used to control the delivery of water into the collector.
In the primary described embodiments, water or an antifreeze solution is used as the working fluid. However, it should be appreciated that a wide variety of other working fluids could be used. By way of example, air could be used as the working fluid if the collectors are used in a space heating application. Such a collector would typically be configured without a storage tank or heat exchanger.
Although only a few embodiments of the invention have been described in detail, it should be appreciated that the invention may be implemented in many other forms without departing from the spirit or scope of the invention. Indeed, it should be appreciated that one of the design strengths of the described thin film collector is that the geometry of the collector, the flow paths within the collector, the size, number and geometry (and in some cases existence) of the storage tanks, risers, manifolds, ports and the other components may be widely varied to meet the needs of a particular application with minimal effort.
It should be apparent that the described thin film collectors can be used in a wide variety of applications. The peripheral welding provides a good seal and the various ports can readily be sealed so that evaporation of the working fluid is minimized during use.
In view of all of the foregoing, it should be apparent that the present embodiments are illustrative and not restrictive and the invention is not limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.
Claims
1. A solar collector, comprising:
- a front sheet formed from a polymer film;
- a middle sheet formed from a polymer film; and
- a back sheet formed from a polymer film, wherein the front, middle, and back sheets are welded together, with the middle sheet being between the front and back sheets, to define a storage tank, a manifold and a front layer of fluid flow channels and a back layer of fluid flow channels, wherein a plurality of longitudinal welds define the fluid flow channels, wherein some of the longitudinal welds are only between the front sheet and the middle sheet to form the front layer of channels and other of the longitudinal welds are only between the middle sheet and the back sheet to form the back layer of channels, wherein each layer of fluid flow channels comprises a plurality of fluid flow channels that extend substantially longitudinally between the manifold and the storage tank, wherein each of the fluid flow channels opens directly into the storage tank, the storage tank being located at a first end of the collector and the manifold being located at a second end of the collector, and wherein the front layer of fluid flow channels provides a hot thermosiphonic flow path therethrough in a first direction and the back layer of fluid flow channels provides a cold flow path therethrough in a second direction, wherein the first and second directions are opposite directions.
2. The solar collector as recited in claim 1, wherein the middle sheet is shorter than the front and back sheets such that the storage tank is formed between the front and back sheets.
3. The solar collector as recited in claim 1, wherein the manifold allows fluid flow between the two layers of fluid flow channels.
4. The solar collector as recited in claim 3, wherein the manifold is formed by a mesh strip attached to a bottom end of the middle sheet.
5. The solar collector as recited in claim 3, wherein the manifold is formed by providing a plurality of holes at a bottom end of the middle sheet.
6. The solar collector as recited in claim 1, wherein the front and back sheets are further welded to define elongated tie down channels on top and bottom ends of the solar collector, the tie down channels being arranged to receive a tie down mechanism and not being in fluid communication with either the storage tank or the fluid flow channels, wherein the elongated tie down channels each have a longitudinal axis that extends substantially perpendicular to the fluid flow channels in a plane defined the fluid flow channels.
7. The solar collector as recited in claim 1, further comprising a heat exchanger disposed in the storage tank, the heat exchanger having an inlet and an outlet at the storage tank.
8. A solar collector, comprising:
- a front sheet formed from a polymer film;
- a middle sheet formed from a polymer film; and
- a back sheet formed from a polymer film, wherein the front, middle, and back sheets are welded together by a plurality of longitudinal welds, with the middle sheet being between the front and back sheets, wherein some of the longitudinal welds are only between the front sheet and the middle sheet to form the front layer of channels between the front and middle sheets and other of the longitudinal welds are only between the middle sheet and the back sheet to form the back layer of channels between the middle and back sheets, wherein each layer of fluid flow channels comprises a plurality of fluid flow channels that extend substantially longitudinally along the solar collector, and wherein the first layer of fluid flow channels provides a flow path therethrough in a first direction and the second layer of fluid flow channels provides a flow path therethrough in a second direction, wherein the first and second directions are opposite directions.
9. The solar collector as recited in claim 8, further comprising a manifold at a bottom end of the collector, the manifold allowing fluid flow between the first layer and second layer of fluid flow channels.
10. The solar collector as recited in claim 9, further comprising a storage tank at a top end of the collector, wherein the fluid flow channels extend longitudinally between the manifold and the storage tank, wherein each of the fluid flow channels opens directly into the storage tank.
11. The solar collector as recited in claim 10, further comprising a heat exchanger disposed in the storage tank, the heat exchanger having an inlet and an outlet at the storage tank.
12. The solar collector as recited in claim 10, wherein the middle sheet is shorter than the front and back sheets to define the storage bank at the top end of the collector, the storage tank being formed between the front and back sheets.
13. The solar collector as recited in claim 8, further comprising a fill port that may be used to facilitate filling the fluid flow channels and the storage tank portions of the solar collector with a working fluid.
14. A solar collector system comprising:
- a front sheet formed from a polymer film;
- a middle sheet formed from a polymer film; and
- a back sheet formed from a polymer film, the back sheet having a substantially same length as the front sheet and the middle sheet being shorter than the front and back sheets wherein the front, middle and back sheets are welded together by a plurality of longitudinal welds to define first and second layers of substantially parallel fluid flow channels that extend longitudinally along the collector, the longitudinal welds on the middle sheet alternate between a weld to the front sheet and a weld to the back sheet, wherein the first layer is between the front sheet and the middle sheet and the second layer is between the middle sheet and the back sheet, and wherein the first layer of fluid flow channels provides a hot thermosiphonic flow path therethrough in a first direction and the second layer of fluid flow channels provides a cold flow path therethrough in a second direction, wherein the first and second directions are opposite directions.
15. The solar collector as recited in claim 14, further comprising a storage tank at a first end of the collector, the fluid flow channels being in fluid communication with the tank and arranged to open into the tank.
16. The solar collector as recited in claim 15, wherein the storage tank is between the front sheet and the back sheet at the first end of the collector to which the middle sheet does not extend.
17. The solar collector as recited in claim 14, further comprising a manifold at a second end of the collector, the manifold allowing fluid flow between the first and second layers.
18. The solar collector as recited in claim 14, wherein the middle sheet extends neither to the top nor bottom end of the collector.
19. The solar collector as recited in claim 14, further comprising a heat exchanger disposed in the storage tank, the heat exchanger having inlet and outlet ports.
20. The solar collector as recited in claim 14, further comprising a glazing layer over the front sheet.
Type: Application
Filed: Apr 24, 2014
Publication Date: Oct 29, 2015
Inventor: Richard O. RHODES (San Francisco, CA)
Application Number: 14/260,988