INCLINED SKYLIT LIGHT WELL
A roof mounted light well oriented to maximize the collection and transport efficiency of solar radiation through an aperture into a building. The device includes a structure having side walls and an upper surface. A light well is located within said structure, and may be partially comprised of said structure. The light well defines a light passageway. The light well is oriented to maximize pass-through of average annualized solar light through said light well. In one embodiment, the light well extends below the roof of the building to a ceiling structure within the building. In some instances, one or both of an upper surface and a lower surface of the light well is horizontal. A reflective element may be provided that projects upwards from the structure. The reflective element may be retractable.
This application claims the benefit of prior filed U.S. Provisional Patent Application No. 61/073,516 entitled “Inclined Skylit Light Well,” filed Jun. 18, 2008, the contents of which are hereby incorporated by reference.
FIELD OF THE INVENTIONThis disclosure relates generally to skylights, particularly those with light wells affixed, wherein the skylights are oriented to maximize average annualized solar light.
BACKGROUND OF THE INVENTIONSkylights typically include a light collecting aperture and a light distributing aperture separated by a structural frame at the roof plane. Light wells connected to a skylight enable illumination to emerge from a location appreciably below the entrance aperture at the roof, as is necessary when the underside of the roof is not the ceiling of the interior space. For example, in a building with a plenum space above a dropped ceiling, the distance between the roof and the ceiling plane can be considerable.
Rooftop skylight systems are becoming increasingly popular as a means to locally displace utility-provided electrical power consumed for interior illumination. While rooftop daylighting is a frequent architectural feature in low rise commercial and residential applications, refinements to technology is improving lighting performance in larger scale commercial and industrial applications, making rooftop daylighting more attractive as an energy efficiency measure, particularly in building types that cannot support vertical glazings, such as big box retail.
In general, skylight applications result in high luminance/illuminance ratios, high contrast levels at the workplane, and widely varying illumination levels throughout the course of the day and the year. The improved uniformity and distribution of illumination that engineered diffuse rooftop daylighting systems provide makes these systems suitable for general interior use where a high degree of lighting functionality is required. However, rooftop daylighting systems that are engineered for maximizing the diffusion of illumination experience a decrease in throughput efficiency because diffusion is accomplished by scattering and absorption within materials and at internal surface boundaries.
Typical rooftop daylighting devices with light wells align the light wells substantially vertically. Typical rooftop daylighting systems, including tubular daylighting devices and splayed light well systems, are typically essentially vertical in nature and are aligned symmetrically about a central vertical axis. Light wells can make turns to avoid obstructions, but they typically terminate at the level of the ceiling substantially orthogonal to the ceiling. That is, light wells are typically designed for equatorial locations where average midday sun position is effectively overhead, and average annualized morning and evening sun position deviates from the light well's axis in one dimension only.
In applications where roof pitch is inclined, skylights are frequently installed parallel to the roof. However, in these applications the light wells attached to these skylights are generally vertically oriented because it's the shortest path to the ceiling. In some applications there may be an arbitrary design solution whereby the light well is also inclined. However, these systems make no clear representation or define a need for maintaining an optimal solar collection angle in order to maximize collection and throughput efficiency. Sometimes these systems incorporate a refractive element in the skylight to redirect solar illumination along the axis of the light well. These refractive elements can improve system performance by enhancing solar collection for a range of sun angles, however they are not optimizing for any location-specific property, and can be applied irrespective to the direction of the axis of a rooftop daylighting system.
In solar photovoltaic technology applications, optimal energy accumulation can be accomplished by tracking of the sun using a dual-axis mechanical system that follows the precise declination and azimuth solar angles. Complexities in the two-axis mechanical system include increased implementation costs that adversely affect payback periods when considering the amount of energy that is received and converted into electricity.
Single axis tracking is generally conceived of as having an adjustable angle of declination, and an azimuthal movement correlated to sun passage along the celestial equator of 15 degrees per hour. Fixed stationary collectors are generally positioned to maximize irradiance relative to other fixed positioning by correlating elevational tilt to its latitude, and orienting its azimuth toward due south. A fixed collection device with an adjustable angle of declination can increase the collection potential of solar irradiance over that of non-adjustable fixed collectors.
Finally, the technique of splaying light well apertures has been demonstrated for centuries. Splaying light well apertures reduces the number of inter-reflections encountered by radiation traveling along the length of a light well. Reducing the number of inter-reflections increases the throughput efficiency of a skylight well, but also reduces the amount of diffusion that occurs along its length, other factors remaining constant. Although this technology improves the optical efficiency of skylight devices, it does so at considerable material expense, in a manner that is complementary to the method proposed in this application, and without any bearing on the improved efficiency by which a skylight well collects and transports sunlight when the transport medium, and aperture of the collection area, is normalized to the average solar declination angle.
SUMMARY OF THE INVENTIONIt is important to maximize the light collection and transport efficiency of these devices in order to maintain favorable economics for zero-energy rooftop daylighting. That is, the cost of rooftop daylight fixtures is frequently offset by the amount of electrical energy that they displace. Since larger units require more material in their construction than smaller units, it is economically preferable to achieve a desired interior lighting level with as small an aperture device as possible. This disclosure posits that a simple manner for accomplishing a sizeable increase in system efficiency, without compromising the system's diffuse lighting performance, is to make an adjustment in the orientation of the lightwell and collection device so that it correlates to an average annualized sun position based on an installation location's latitude.
This disclosure introduces a conceptual solar-mechanical improvement that is applicable to all rooftop daylighting systems, regardless of whether they are tubular, rectilinear, or splayed, and that maximizes collection and transport efficiencies of solar radiation.
A skylight's curb and well typically protrude above and below the roof plane. Therefore, the solar collection aperture of the light well can be optimized for the average angular direction of the incoming solar energy. For increasing the admittance of solar radiation through a 3-dimensional aperture of set dimensions in the roof plane, the light well can be inclined to the south. On an averaged annualized basis it can be shown that, at locations other than at the equator, an inclined rooftop daylighting unit will collect and transport more solar energy than a vertically aligned combination, other factors remaining constant. Since the light well is sufficiently oriented toward an averaged annualized sun angle position, light well efficiency will increase because collected solar radiation will undergo fewer interreflections than it would through a vertically aligned light well.
Fixed solar collection devices can be oriented due south with an angle of declination (inclination) equal to the latitude of the installation, and if adjustable, an orientation of the collection device can be increased by as much as 23 degrees in winter and decreased by as much as 23 degrees in summer to account for the seasonal changes in the path of the sun. Another solar optimization model refers to using an angle equal to 0.9*(angle of latitude)+29 degrees for fixed collection devices, and if adjustable, with optimization angles equal to the latitude minus 2.5 degrees for spring and fall, with summer angle equal to 52.5 degrees less than the winter angle.
The roof mounted device of the invention for maximizing the admittance of solar radiation through an aperture into a building includes a structure having side walls and an upper surface. A light well is located within said structure. The light well defines a light passageway. The light well is oriented to maximize pass-through of average annualized solar light through said light well. In one embodiment, the light well extends below the roof of the building to a ceiling structure within the building. In some instances, one or both of an upper surface and a lower surface of the light well is horizontal. A reflective element may be provided that projects upwards from the structure. The reflective element may be retractable.
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Light well 30 is located within structure 16 and extends below roof 14. Light well 30 defines light passageway 32. Light well 30 extends below roof 14 to ceiling structure 40. Light well 30 defines a solar collection aperture 36 at an upper end and a lower or exit aperture 38 at a lower end. In one embodiment, light well 30 is trimmed at an upper end to have a horizontal surface. In other embodiments, light well 30 may be trimmed at the lower end so that the lower end of light well 30 is flush with ceiling structure 40.
Light well 30 may be oriented to maximize average annualized solar light, as can be seen in
The first embodiment of the invention orients solar collection aperture 36, structure 16 and light well assembly 30 toward the south for averaged maximization of solar energy collection (
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As an exemplary implementation of the optimized inclined light well of the invention, for a latitude of 32.79 degrees N as illustrated in
The maximum solar elevation for any day occurs at 12:00 solar noon. For the location shown, this corresponds to a 33 degree maximum solar elevation on December 21 and an 81 degree solar elevation on June 21. The average annualized noon solar elevation is 57 degrees, shown as point B. Orienting light well 32 of the collector 10 so that the angle of inclination of light well 32 correlates with the Average Annualized Solar Position maximizes the average annualized flux transferred through the device.
Potential energy density is highest when the sun is directly overhead. However, in northerly or southerly latitudes, the sun is directly overhead less frequently, if ever. Since energy density increases when the angle of incidence is normal to the receiving surface, an object or aperture would need to be inclined in order to receive maximum potential energy density.
It is well known that the energy falling on or through a one square meter aperture parallel to the Earth's surface can reach or exceed 1 kilowatt, for an intensity of 1 kw/square meter, and that energy density falling on this same surface is maximized when the surface is perpendicular (orthogonal) to the sun's rays.
For any geographic location, the sun's position can be accurately described for any point in time by two values: 1) Solar Elevation, which describes an angular altitude, and is defined as the angle between the sun and an idealized horizon, and 2) an Azimuthal angular value, which defines the angular position of the sun during the movement of the sun from the East to West, and is 180 degrees for any geographic location at 12 solar noon.
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It is, therefore, an object of the current invention to install inclined, roof mounted, daylight systems optimized to maximize collection and transport efficiencies of solar radiation.
Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the claims.
Claims
1. A roof mounted device for maximizing the admittance of solar radiation through an aperture into a building, said device comprising:
- a structure having side walls and an upper surface;
- a light well within said structure said light well defining a light passageway;
- wherein said light well is oriented to maximize pass-through of average annualized solar light through said light well.
2. The building mounted device according to claim 1 wherein:
- said light well extends below the roof of the building to a ceiling structure within the building.
3. The building mounted device according to claim 1 wherein:
- said light well is offset from vertical.
4. The building mounted device according to claim 1 wherein:
- one of said upper surface and a lower surface of said light well is horizontal.
5. The building mounted device according to claim 1 further comprising:
- a reflective element projecting upwards from said structure.
6. The building mounted device according to claim 5 wherein:
- said reflective element is retractable.
7. The building mounted device according to claim 1 wherein:
- an outer surface of said structure protruding above the roof defines a curb.
8. The building mounted device according to claim 1 wherein:
- an outer surface of said light well protruding above the roof defines a curb.
9. The building mounted device according to claim 1 wherein:
- said light well is rotatable.
10. The building mounted device according to claim 9 wherein:
- said light well rotates to a predetermined orientation correlated to a time of year.
11. The building mounted device according to claim 1 wherein:
- said light well has a cross-sectional shape selected from a group consisting of round, square, rectangular and octagonal.
12. A method of maximizing the admittance of solar radiation through an aperture into a building comprising the steps of:
- locating a roof aperture in a roof of a building;
- positioning a light well to extend above and below said roof aperture, said light well defining a passageway that passes through said aperture, said light well having a solar collection aperture at a first end and an exit aperture at a second end, said light well defining a longitudinal axis;
- orienting said longitudinal axis of said light well at an angle that substantially maximizes pass-through of average annualized solar light through said light well passageway.
Type: Application
Filed: Jun 18, 2009
Publication Date: Dec 24, 2009
Inventor: Kurt Levens (Borrego Springs, CA)
Application Number: 12/487,435
International Classification: E04D 13/035 (20060101);