Patent Application
20110232634
The subject matter herein relates generally to solar heating systems. More particularly, the subject matter disclosed herein relates to an improved heating coil for use in flat panel solar collectors.
The ever increasing costs associated with conventional heating systems as well as global concerns regarding greenhouse gas emissions have fueled intense interest in cheap, clean solar energy solutions. Conventional solar powered heating systems typically employ flat panel solar collectors having a heating coil through which water is circulated. Cool water is pumped into the solar panel where energy from the sunlight incident on the solar panel warms the heating coil, which, in turn, transfers heat to the water flowing within it. The heated water then exits the solar panel and is then used, stored in an insulated storage container for later use, or run through a heat exchanger where the captured heat is again transferred to another medium.
Although solar heating technologies have existed for many years, drawbacks to conventional solar heating systems have hampered wide scale adoption of the technology. For example, due to their inefficiencies, conventional solar heating systems require significant surface area coverage in order to generate sufficient volumes of heated fluid. This necessitates using either large solar panels or groups of smaller solar panels for which initial installation and maintenance costs can be high. Various attempts have been made to improve the efficiency of conventional solar panels, such as the use of heating coils with modified geometries that increase the heat transfer surface area of the coil to improve overall heat absorption by the fluid, but such systems still exhibit drawbacks. For example, some hot water solar panels employ heating coils made of tubes having an elliptical cross section, as opposed to a rounded cross section, that are aligned in a side-by-side configuration and interconnected with a header on each end. Water is forced into one header, which directs the water through each of the tubes and into the other header where it then exits the panel. As such, although the modified structure of the heating coil works to improve heat transfer, the overall configuration, which only allows water to flow across the panel once in a single direction, leaves the overall efficiency of the panel low.
Additionally, the use of complex, custom designed components in many conventional solutions requires complicated interconnections between fluid transmitting parts, increasing initial manufacturing and installation costs, as well as long term maintenance costs. Another drawback to conventional systems is that consumers are often deterred by the aesthetic impact the large, and often numerous, solar panels have on their property.
It would be advantageous to provide a flat panel solar collector that provides better heating efficiency per square foot of panel coverage, and that has low installation and maintenance costs
An apparatus for heating a fluid using solar energy is disclosed, in one embodiment comprising an absorption plate exposed to the solar energy, and a heating coil, the heating coil comprising a first lateral tube comprising a cylindrical first end portion, a cylindrical second end portion, a flattened top portion, and a flattened bottom portion, the flattened bottom portion being in contact with the absorption plate, a second lateral tube comprising a cylindrical first end portion, a cylindrical second end portion, a flattened top portion, and a flattened bottom portion, the flattened bottom portion being in contact with the absorption plate, and a cylindrical end cap connecting the second end portion of the first lateral tube to the second end portion of the second lateral tube such that fluid flowing through the first lateral tube in a first direction is redirected by the end cap into the second lateral tube in a second direction. In one embodiment the heating coil can be comprised of a single piece of continuous conduit, while in other embodiments the heating coil can be comprised of multiple pieces of conduit that have been joined together.
So that the manner in which the features of the invention can be understood, a detailed description of the invention may be had by reference to certain embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the drawings illustrate only certain embodiments of this invention and are therefore not to be considered limiting of its scope, for the scope of the invention encompasses other equally effective embodiments. The drawings are not necessarily to scale, emphasis generally being placed upon illustrating the features of certain embodiments of invention. Thus, for further understanding of the invention, reference can be made to the following detailed description, read in connection with the drawings in which:
An absorption plate 120 can be attached to one of the open sides of the frame 110 so that the side the absorption plate 120 is attached to is enclosed while the opposite side is left open, forming an open box-like structure. Energy from sunlight 250 incident on the solar collector 100 is absorbed by absorption plate 120, which converts the light energy into heat. Located within the frame 110 and on the surface of absorption plate 120 that faces the open portion of the solar collector 100 can be a heating coil 150. In one embodiment, heating coil 150 can be a single, hollow conduit that can have a coil inlet 165 on one end, and that can extend longitudinally in a serpentine pattern between the frame bottom 114 and the frame top 112 to a coil outlet 175 located on the opposite end of the heating coil 150 from the coil inlet 165. In other embodiments, heating coil 150 can extend in a serpentine pattern between frame sides 111 and 113, or in other geometries within the solar panel 100. Heating coil 150 can be held in place by one or more braces 140 that, in one embodiment, can be laid over the heating coil 150 and physically or chemically attached to the frame and/or the absorption plate 120 by, for example, rivets, screws, or epoxy, such that the heating coil 150 is securely held in place between the brace 140 and the absorption plate 120.
In another embodiment, heating coil 150 can comprise two or more lateral tubes 158 aligned in a substantially parallel spaced apart arrangement, for example, with the spacing between the lateral tubes 158 being two and one-half to three inches. In other embodiments, the size and spacing of the coils can be varied to alter the amount of sunlight 250 incident on the absorption plate 120, thereby altering the performance characteristics of the solar panel 100 to meet specific design requirements. For example, closer spacing of the lateral tubes 158 will reduce the amount of sunlight incident on the absorption plate 120 and vary the amount of sunlight 250 incident directly on the lateral tubes 158, thereby increasing heat absorption on the tops of the lateral tubes 158 and decreasing the amount of heat absorption from the absorption plate 120 on the bottom of the lateral tubes 158.
The coil inlet 165, which can be a rounded pipe or tube, interconnects with one end of the first lateral tube 158 in the heating coil 150. The ends of each of the lateral tubes 158 are connected by a rounded end cap 155 so that fluid flowing in one direction through a lateral tube 158 can be routed in a different direction and into an adjacent lateral tube 158. The free end of the last lateral tube in the coil is interconnected with the coil outlet 175, which can be a rounded hollow conduit, such as a pipe or tube. The coil inlet 165 passes through a collector inlet 160, which can be a hole extending through one of the sides of the frame 110, while the coil outlet passes through a collector outlet 170, which can also be a hole extending through one of the sides of the frame 110. Accordingly, fluid can enter the heating coil 150 through the coil inlet 165, travel in a first direction along the first lateral tube 158, exit the opposite end of the first lateral tube 158, and flow through the end cap 155 which routes the fluid in a different direction into the adjacent lateral tube 158. The fluid then flows back and forth along the subsequent lateral tubes 158 and end caps 155 until it reaches the coil outlet 175 and exits the heating coil 150. In one embodiment, a hot fluid inlet returns the heated fluid to the storage tank 200, where the heated fluid is stored until needed, at which time the hot water can exit the storage tank 200 through a hot fluid outlet.
In other embodiments, rather than directly heating the fluid within storage tank 200, solar heating system 10 can further comprise a heat exchanger located between the solar collector 100 and the storage tank 200 through which heated fluid from the solar collector 100 travels in order to transfer heat to the fluid contained in storage tank 200. For example,
End caps 155 can be hollow rounded conduits, for example tubes or pipes having a rounded cross section that, in one embodiment, are semi-circular in shape such that fluid entering one end of the end cap 155 is directed in a different direction upon exiting the end cap 155. The diameter of each end cap 155 can be such that it either fits snugly within or around the ends of each of the lateral tubes 158 to facilitate easy interconnection of the two parts by physical or chemical means, for example brazing or PVC cementing. In one embodiment, end caps 255 can be a single piece of conduit. In other embodiments, end caps 155 can be comprised of more than one piece of hollow conduit joined by physical or chemical means to redirect the fluid flow, for example, combinations of elbow joints and straight sections that render a shape to the end cap 155 that may not be semi-circular. Similarly, coil inlet 165 and coil outlet 175 can be rounded hollow tubes of such a diameter that they can be fit snugly within or around the ends of lateral tubes 158 to facilitate easy interconnection of the two parts by physical or chemical means, for example brazing or cementing. The rounded ends of lateral tubes 158 and rounded cross sections of end caps 155 facilitate easy and reliable interconnection of the components without the need for specialized components requiring expensive custom designs and manufacturing.
In some embodiments, heating coil 150 can be a single, continuous piece of conduit with selectively flattened regions in the locations corresponding to where the lateral tubes 158 would be. In other embodiments, heating coil 150 can be a single, continuous piece of flattened conduit in which the entire coil exhibits an elliptical cross section.
The flattened bottom 154 of the lateral tube 158 provides maximum surface area for heat transfer between the absorption plate 120 and the heating coil 150. Likewise, the flattened top 152 of the lateral tube 158 provides maximum surface area for exposure to sunlight 250, thereby providing maximum heating of the top surface of the heating coil 150. The elliptical cross section of lateral tube 158 also increases the surface area of fluid that is exposed to a heated interior wall surface within the heating coil 150. Accordingly, the flattened serpentine heating coil 150 not only maximizes the surface area of the heating coil 150 that is heated by the solar collector, but also maximizes the surface area of the fluid within the coil that is exposed to the heated coil, thereby improving the overall heat transfer efficiency of the solar collector. Furthermore, the serpentine path in which the fluid within the heating coil travels within the solar collector 100 keeps the fluid within the solar collector 100 for a longer period of time, increasing heat absorption by the fluid. The novel structure of the heating coil 150 therefore exposes a high volume of water to a high amount of heated surface area for a long period of time, thereby improving the heating efficiency of the solar collector 100.
For example, a conventional flat panel solar collector of average size, for example twenty inches wide by six feet long, typically provides about 750 BTU of heating output per square foot of panel coverage, resulting in an average rise in fluid temperature of about 2° F. per pass through the solar collector. Similarly sized flat panel solar collectors embodying the present design can produce up to 1,600 BTU per square foot of panel coverage, resulting in an average rise in fluid temperature of about 8° F. per pass through the solar collector 100. This increased performance and heating efficiency can reduce the amount of coverage needed to produce the same degree of fluid heating. For example, in a residential hot water heating application, a typical conventional system requires approximately four twenty inch by six foot solar collectors to provide sufficient hot water for one to two adults. Embodiments of the present design can produce the same hot water output using only two solar collectors of the same size, thereby reducing initial installation costs, reducing long term maintenance costs, and reducing the aesthetic impact of the solar collectors being installed on the owner's property, typically the roof.
Different embodiments of the invention can incorporate additional features to improve the performance of the invention, including coating the absorption plate 120 and heating coil with materials to increase sunlight absorption, such as black paint, insulating the solar collector 100 with thermally protective materials, and enclosing the side of the solar collector 100 through which sunlight enters with a transparent covering, such as glass, to reduce thermal loss from wind and other environmental factors. In other embodiments, the solar collector 100 can be configured in an inverted manner such that the bottom of the absorption plate 120 faces the incident sunlight 250.
The above detailed description is provided to illustrate exemplary embodiments and is not intended to be limiting. Although the solar heating system 10 has been shown and described with respect to various embodiments, it will be apparent to those skilled in the art that numerous modifications and variations within the scope of the present invention are possible. For example, numerous other materials can be used within the scope of the exemplary structures described as will be recognized by those skilled in the art. Additionally, although various geometries have been used to describe various embodiments of the invention, it will be recognized by those of skill in the art that other arrangements and geometries of the components can be equally effective.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
