US20090313918A1

US20090313918A1 - Inclined skylit light well

Info

Publication number: US20090313918A1
Application number: US12/487,435
Authority: US
Inventors: Kurt Levens
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-06-18
Filing date: 2009-06-18
Publication date: 2009-12-24

Abstract

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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

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 INVENTION

This 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 INVENTION

Skylights 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 INVENTION

It 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.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a conventional skylit light well construction showing penetration of the roof plane with a light well that has a depth that terminates at a ceiling plane location.

FIG. 2 shows a light well having a 15 degree southerly rotation to normalize (maximize) solar collection for a given roof plane aperture size at 15 degrees north latitude.

FIG. 2A shows a top view of the device of FIG. 2A having a rectangular light well.

FIG. 2B shows a top view of an alternate embodiment of the device of FIG. 2A wherein the light well has a square cross-section.

FIG. 2C shows a top view of an alternate embodiment of the device of FIG. 2A wherein the light well has a circular cross-section.

FIG. 2D shows a top view of an alternate embodiment of the device of FIG. 2A wherein the light well has an octagonal cross-section.

FIG. 3 shows a horizontal trimming of interior aperture for horizontal placement of an illumination distribution element.

FIG. 4 shows a horizontal trimming of an exterior aperture for horizontal placement of skylight dome and also a rear reflective element for increasing winter collection.

FIG. 5 shows a finished form illustrating inclined well walls and horizontal apertures.

FIG. 6 shows a predicted solar output of a typical fall day at 9:30 a.m. wherein an inclined well shows greater non-reflected light pass-through.

FIG. 7 shows a predicted solar output of a typical fall day at 12:00 p.m. wherein an inclined well shows greater non-reflected light pass-through.

FIG. 8 shows a predicted solar output of a typical fall day at 2:30 p.m. wherein an inclined well shows greater non-reflected light pass-through.

FIG. 9 shows a predicted solar output of a typical winter day at 10:00 a.m. wherein an inclined well shows greater non-reflected light pass-through.

FIG. 10 shows a predicted solar output of a typical winter day at 2:00 p.m. wherein an inclined well shows greater non-reflected light pass-through.

FIG. 11 shows a predicted solar output of a typical spring day at 12:00 p.m. wherein an inclined well shows greater non-reflected light pass-through.

FIG. 12 shows a predicted solar output of a typical summer day at 12:00 p.m. wherein an inclined well shows a generally equal non-reflected light pass-through.

FIG. 13 is an annual sunpath chart for San Diego, Calif., at latitude 23.89, showing a Zone of Maximum Collection and Throughput for solar collection superimposed upon the collection axis of the vertically aligned light well and the averaged direction of sunlight.

FIG. 14 shows an annual sunpath chart for San Diego, Calif. at latitude 23.89. A Zone of Maximum Collection and Throughput that is 23 degrees to either side of the main axis of an inclined light well is superimposed upon the axis of average annualized sun position demonstrating much better correlation.

FIG. 15 is a schematic diagram showing the relationship between sunlight intensity and angle of incline for sunlight incident upon a surface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 through 12, shown is a building mounted device 10, provided for the admittance of solar radiation into building 12. Device 10 is supported by a roof 14. A structure 16 is mounted on roof 14. Structure 16 includes north side wall 18, south side wall 20, east side wall 22 and west side wall 24. Structure 16 additionally preferably includes upper surface 26 for supporting skylight 28.
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 FIGS. 2-12. Fixed solar collection devices can be oriented due south with an angle of declination (inclination) correlated to the latitude of the installation.
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 (FIG. 2). Structure 16 extends above roof 14 to form a curb. Structure 16 may be constructed to have an upper surface 26 that is coplanar with skylight 28 or where skylight 28 protrudes above an upper surface 26 of structure 16. Additionally, light well 30 may extend above roof 14 to form a curb. For purposes of this application, “curb” shall be defined as an exterior surface of a structure protruding from roof 14. The shift in orientation of aperture 36, and light well 30 will couple more incident solar radiation than a vertically oriented shaft of the same dimensions. This orientational shift will enable flux transfer through light well 30 with increased efficiency because, on an averaged annualized basis, rays of radiation will undergo fewer bounces prior to reaching the exit or lower aperture 38 of device 10. Apertures 36, 38 and shaft of light well 30 having a rectilinear cross-section are shown in FIGS. 2-12. However, as shown in FIGS. 2A-2D, circular cross-sections, square cross-sections, octagonal cross-sections, or other cross-sectional geometries and tubular forms may also be used.
As shown in FIG. 2, device 10 may be constructed to be rotatable. For example, structure 16 and attached light well 30 may be mounted on roof 14 via rotatable base 39. Rotatable base 39 may be motorized and automated. Rotatable base 39 may be user controllable or may rotate to a predetermined orientation dependent upon the time of year or site orientation of building. Where the curb and light well are structurally distinct, and where the curb is oversized so that the light well may be repositionable within the curb, the light well can be oriented such that its central axis is different from the central axis of its curb.
FIG. 3 is another embodiment of the disclosure, which for cosmetic reasons adjusts exit aperture 38 of the device to be parallel to an interior floor, e.g., ceiling structure 40.
FIG. 4 is an embodiment in which northerly wall 18 remains in place for reflecting southerly solar illumination into aperture 36. The northerly wall extension 42 will shade device 10 during summer, decreasing its throughput efficiency in summer months. However, northerly wall extension 42 may be retractable, thereby increasing the solar efficiency that could be achieved annually by seasonal adjustments. The northerly wall extension will shade the device during summer, decreasing its throughput efficiency in summer months. However, if the northerly wall extension is made retractable, then increases in solar efficiency may be achieved annually by seasonal adjustments.
FIG. 5 is another embodiment of the disclosure, in which the entrance aperture 36 and exit apertures 38 are both horizontal and parallel to building surfaces, e.g., ceiling structure 40 and roof 14. The throat diameter perpendicular to the axis of light well 30 is the same as a comparable vertical light well. The side walls 22, 24 become parallelogram in shape.
FIGS. 6-12 show a predicted solar output of an optimized vertical well 10B modeled for various times and seasons throughout the year. Non-reflected light pass-through is indicated by light area 50B that is the result of non-reflected pass-through through vertical well 10B. Light area 50A is the result of non-reflected pass-through through inclined well 10A. Light areas 50A and 50B are surrounded by a shadow image projected from roof sections surrounding wells 10A and 10B. Note that in each of FIGS. 6-11, in general the greater non-reflective pass-through, as indicated by light areas 50A as compared to 50B, is associated with the use of optimized inclined well 10A.
In particular FIG. 6 shows a comparison of vertical light well 10B and optimized inclined light well 10A on September 26th at 9:00 a.m. It can be seen that the light area 50A associated with the optimized light well 10A shows greater non-reflected pass-through as compared to light area 50B of vertical light well 10B.
Referring now to FIG. 7, it can be seen that light area 50A is larger than light area 50B, which indicates a greater non-reflective pass-through of light through optimized inclined well 10A as compared to vertical inclined well 10E on September 26^that noon.
Referring not to FIG. 8, light area 50A can be seen to be larger than area 50B, which indicates a greater non-reflective pass-through through inclined well 10A as compared to non-reflective pass-through through vertical light well 10B on September 26^that 2:30 p.m.
Referring to FIG. 9, light area 50A can be seen showing a non-reflective pass-through through optimized inclined light well 10A. In comparison, no non-reflective pass-through is indicated through vertical light well 10B on November 16^that 10:00 a.m.
Referring now to FIG. 10, shown is a light area 50A indicating non-reflective pass-through through optimized inclined light well 110A. In contrast, no non-reflective pass-through is indicated to pass through vertical light well 10B on November 16^that 2:00 p.m.
Referring now to FIG. 11, shown is a comparatively larger light area 50A as compared to light area 50B. Light area 50A indicates a non-reflective pass-through through optimized inclined light well 10A. Relatively smaller light area 50B indicates less non-reflective pass-through of vertical light well 10B on March 12^that noon.
Referring now to FIG. 12, shown are light squares 50A and 50B of approximately equal size indicating about the same non-reflective pass-through through each of optimized inclined light well 10A and vertical light well 10B on July 24^that noon.
As an exemplary implementation of the optimized inclined light well of the invention, for a latitude of 32.79 degrees N as illustrated in FIG. 13, the maximum solar elevation for each time of day occurs at the summer solstice as defined by sun path xx, and the minimum solar elevation of the sun for each time of day occurs on the winter solstice as defined by sun path yy. A sun path averaged between these two, zz, represents an average solar elevation path, whose intensity of incoming solar radiation is an average of that of the solstices for each time of day, which for every geographic location can be specified as occurring on the equinoxes, September 21 and March 21.
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.
Referring now to FIG. 15, sunlight is shown landing on a 1.15 square meter surface parallel to the Earth's surface. For a 30 degree incline, cos 30=1/X, where x=1.15. This equates to an increase in energy density of 1/0.86=15%, since a smaller surface oriented orthogonally to the sun can collect all of the energy contained wherein.
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.