Method and apparatus for a passive solar day lighting system

Optical: systems and elements – Mirror – Plural mirrors or reflecting surfaces

Reexamination Certificate

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C359S869000, C359S591000, C359S593000

Reexamination Certificate

active

06299317

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method and apparatus for a passive solar day lighting system using sunlight transported into a structure through an optical conduit. More particularly, the present invention is directed to a passive lighting system that does not require active tracking of the sun and utilizes non-imaging optical collectors for concentrating collected sunlight and optical fibers for transporting light to a light fixture in a room.
2. Description of Prior Art
The use of natural light in buildings can significantly reduce the energy consumption and improve the quality of life. But interior rooms cannot benefit from a window or a sky light and only rooms immediately below a roof can enjoy a skylight. There have been several efforts to capture sunlight and deliver it to remote parts of buildings using fiber optics or light pipes or optical conduits.
Many of these previous efforts used some type of active sun tracking system coupled with complicated lens and mirror systems. For example, U.S. Pat. Nos. 4,246,477; 4,297,000 and 4,409,963 disclose various sunlight collectors, containing Fresnel lens systems. The collectors are mounted on the roof of a building and actively track the sun during daylight hours.
Other systems for collecting and transporting sunlight are disclosed in U.S. Pat. Nos. 4,307,936; 4,541,414; 4,539,625; 5,548,490 and 5,709,456. These patents disclose various devices to collect sunlight without actively tracking the sun. The U.S. Pat. Nos. 4,307,936 and 4,541,414 are directed to sunlight collecting devices that use a parabolic collector to capture sunlight and a complex arrangement of lenses to concentrate the captured sunlight. The U.S. Pat. Nos. 4,539,625; 5,548,490 and 5,709,456 are directed to large stack luminescent or fluorescent sheets arranged to collect sunlight and convert that collected light into concentrated light.
Some of these approaches have used complex, delicate systems that track the sun actively. The other systems, require either complicated mirror and lens assemblies or specialized glass collectors having luminescent or fluorescent dyes therein, making the systems so expensive that they cannot be justified by the electric energy it saves.
Passive solar tracking systems are known in the prior art. These passive tracking systems generally use solar thermal energy to track the sun's path. Solar thermal powered tracking systems are described in U.S. Pat. Nos. 4,332,240; 4,262,654; 5,600,124; 4,175,391; 4,275,712; 4,306,541 and 4,476,854. In each of these patents, a parabolic trough collects solar energy and heats fluid-containing reservoirs to cause differential vaporization and shifting of fluid to rotate the apparatus. These passive tracking systems offer a cheaper means for tracking the sun, however, the size of the collectors renders them generally unsuitable for a large scale device.
SUMMARY OF THE INVENTION
The present invention contemplates a simple sunlight collection system based on the premise that the cost of collecting and transporting sunlight should be low. Therefore, a high-precision tracking feature is not part of the present invention. Important elements required for a day-lighting system are the means to collect sunlight and the means to transport the collected light to the building interior space. The present invention is a passive system without active tracking of the sun and utilizes well established non-imaging optical collectors for concentrating the sunlight and optical fibers for transporting light to a light fixture in a room. The use of optical fibers (plastic or comparatively less expensive glass) that are flexible, minimizes cost of installation in comparison to light pipes or other optical guides.
To meet these and other objectives, the present invention is directed to a passive solar day-lighting system using a low light concentration ratio sun-light collection system. The collection system includes an array of non-imaging concentrators housed in an enclosure with at least one transparent surface. The sun-light collection system is mounted on a passive solar thermal tracking system and is connected to an optical conduit which transports collected and concentrated light from the sun-light collection system to an interior building space.
The solar collector system as contemplated in the present invention has a low light concentration ratio of at least 50, and no greater than 700. The concentration ratio or factor is the ratio of the inlet area to the exit area of the collector. The higher the concentration ratio, the lower is the half-angle of acceptance and hence the higher is the precision required for tracking the sun. Because the array of non-imaging concentrators has a relatively low concentration ratio, the system does not require precision tracking.
In certain preferred embodiments of the invention, the array of non-imaging concentrators is a plurality of conical compound parabolic concentrators, each of the concentrators having a predetermined input half-angle and a predetermined exit-half angle. Each of the plurality of conical compound parabolic concentrators also has a predetermined input diameter and a predetermined exit diameter, and the sun-light collection system is designed by optimizing the predetermined input half-angle, the predetermined exit-half angle, the predetermined input diameter, and the predetermined exit diameter of each of the plurality of conical compound parabolic concentrators.
In certain preferred embodiments of the invention, the array of non-imaging concentrators alternatively is an array of Fresnel lenses of square or rectangular shape, and may be manufactured singly or on integrally on a single sheet of plastic. It is also contemplated that the array of non-imaging concentrators may be comprised of a plurality of sets of two concentrators in tandem with a Fresnel lens as a primary concentrator and a conical compound parabolic concentrator as a secondary concentrator.
The optical conduit according to certain preferred embodiments of the present invention is a series of optical fibers coupled to exit ends of each non-imaging concentrator. The optical fibers can be made of a plastic material or an inexpensive glass.
The passive solar thermal tracking system contemplated by certain preferred embodiments of the invention includes a non-electric tracking device that uses solar thermal energy to power a device to move the collector thereby tracking sun movement. The contemplated solar thermal tracking system should have an inaccuracy of no more than 5° while tracking the sun. This requires a half angle of acceptance of no more than 5° for the primary collector.
The present invention is also directed to a method for passively supplying sunlight to a day-lighting system. The contemplated method includes forming a low light concentration ratio sunlight collection system by arranging an array of non-imaging concentrators, each having an input end and an exit end in an enclosure with at least one transparent surface. The method also includes mounting the array of non-imaging concentrators on a passive solar thermal tracking system.
Preferred embodiments of the method according to the invention further include connecting an optical conduit to each exit end of the array of concentrators, and passively tracking the sun using the solar thermal tracking system, thereby collecting sunlight in the array of non-imaging concentrators. The method further contemplates transporting the collected sunlight through the optical conduit to an interior portion of a structure.
The significance of passive solar powered tracking system is it does not require external power and it is less costly than powered active systems. Another advantage is solar powered tracking systems is proven and is commercially available for photovoltaic applications (e.g., from Zome Works Corp. Albuquerque, N. Mex. 87125). With existing controls, electric lighting can be easily integrated with the day-lighting based on the present invention, and can be con

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