STUDY OF LIGHT SHELF AND RESULTING ILLUMINATION LEVEL INSIDE SPACE FOR MALDIVES AND MOSCOW REGION
BACKGROUND
INTRODUCTION
The objective of this paper is to understand and highlight the effectiveness of light shelves in different geographical region and their effect in illuminance level inside the space. Daylight simulations were performed for a custom light shelves (plastic material) for a typical space in two different location - 1) Moscow, Russia and 2) Male Hulelu, Maldives. Moscow, in Russia, is located at 55.7 degree latitude and Male Hulelu, in Maldives, is located at 4.2 degree latitude. Simulations were performed using Ecotect and Radiance and weather data for both the space were taken from U.S Department of Energy website. Simulation readings were taken both for sunny as well as overcast sky, during 21st of March, June and September. For Maldives, readings are taken at 9 AM, 12 PM and 3 PM of day and for Moscow, readings were taken at 9 AM, 12 PM and 5 PM. Along with variation in day and time, reading were also taken having variation in location of light shelf - both side of wall (inside and outside), only exterior side of wall and only interior side of wall and compared with same situation of day and time without light shelf. The space taken for study was a small room with dimensions of 4.5 M x 6 M with height of 3 M. The smaller faced with width of 4.5 M faces south and has a opening and light shelf. No opening are there on other sides - East, West and North. Height of light shelf is 2.1 M from ground and is 0.6 M in width both inside and outside the wall. Length of light shelf is 3.9 M and is centrally placed on the facade of 4.5 M leaving wall edges of 0.3 M both the sides. Illumination range inside the space is not tried to be maintained in specific range of comfort. It is used in pure form as obtained by the conditions available. Analysis grid for the space is divided into grid of 21 x 17 units with 21 units at facade of 4.5 M width. Analysis of results is based only for the central grid and not any other portion of the grid, and hence space.
The light shelf is a classical daylighting system, to control and distribute sunlight and skylight, reduce glare, and improve the interior illuminance in side-lit rooms. (Christoffersen 1995, littlefair 1996). Light shelves are the horizontal devices which help to reflect light from window towards the ceiling and penetrate little deep in the space. Light shelves are designed to shade and reduce sunlight and skylight near the window, and reflect light from its top onto the ceiling. They have high reflective top surface to enhance the reflection of light towards the ceiling. Light shelves are typically used in big bulky buildings where it is difficult for light to penetrate deep inside or places where sky is over casted most of the time. IMPORTANT: LIGHT SELF BOUNCE LIGHT FROM SHELF TO CEILING WHICH THEN GETS BOUNCE TO THE PERIMETER ZONE ONLY AND NOT AT THE BACK WALL.
APPLICATION
Illuminance Level, Light shelves, Sunny Sky, Overcast Sky, With Light Shelf, Without Light Shelf.
• Light shelves require direct sunlight. The windows should face the sun for a larger fraction of time that the space is occupied. As a result, they are more advantages to place on windows facing equator. • They are generally mounted with window having large area of glazing over the height of 2.1 m (7 ft.). • The glazing that directs light on the light shelves is required to be clear glass, in order to receive sufficient light to reflect. Tinted or Colored glass reduces the intensity of income light. More smoother the surface, more will be the reflection. • Depending on quality of light required, finishing layer of light shelves and the ceiling can either be smooth or rough.
STUDY MODEL
LIMITATIONS
KEYWORDS
• The extension of light shelves inside the room may result in interface with sprinkler system. In Canada, they cannot exceed 1200 mm (4 ft.) in width if sprinklers are present or the design will require integration with sprinkler system to cover the floor area under the light shelf. • The illumination range and level inside the space depends both on time of day and year and also on sky conditions. • Light shelves needs regular maintenances in terms of cleaning in order to have proper and sufficient reflection of light off the shelf to the ceiling.
ELEMENTS INVOLVED • • • •
ARCHITECTURE 632 006 - DAYLIGHTING
Light Shelf - Reflector Window Ceiling Shading device(s)
SCHOOL OF DESIGN
UNIVERSITY OF PENNSYLVANIA
LIGHTING PATTERN OF THE LIGHT SHELF SYSTEM
CASE STUDY - NREL Campus, Colorado
• The pattern of illumination depends on the reflection characteristics of the light shelf, and it depends on the geometry and reflection characteristics of the ceiling surface. • If the reflection by the light shelf is specular, the reflection is controlled by the law of optics where reflection equals the angle of inciLight shelf and system dence. • If the sun is low in the sky, sunlight penetrates deeply into the space. If the sun is high, the ceiling is illuminated close to the wall. • Pure specular reflection creates a sharply defined rectangular bright spot on the ceiling. This might be bright enough to annoy occupants. This effect can be reduced by making the reflecting surface of light shelf more diffuse. Hence light spreads out on the ceiling. • If the reflection is very diffuse, penetration into the space is sacrificed. A taller ceiling provides deeper light penetration, and it also distributes the light more widely within the space. High sun angle – Less penetration • Under overcast sky, the light shelf reduces the illumination level on and more intensity the working plane because it directly cuts off part of view to the sky. • The magnitude of reduction at a given point depends on the distance from the light shelf and the position and depth of the light shelf. • An interior light shelf at normal height would thus screen off most of the light from the sky on the working plane in the middle of the room, while an exterior light shelf would do this mostly in the area just inside the window. Low sun angle – More penetration and less intensity
STUDY REGION A) COLORADO US LATITUDE - 39.74 B) MOSCOW RUSSIA LATITUDE - 55.7
C A TROPIC OF CANER
EQUATOR
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ARCHITECTURE 632 006 - DAYLIGHTING
C) MALE ISLAND MALDIVES LATITUDE - 4.2
• • • • • •
100% of the workstations are daylit No employee is more than 30 feet of the window Daylighting controls that works Manual on, manual off with vacancy sensors and local dimming controls in all daylit zones. Run dark at night, including most emergency lighting - less than 5% of lights on at night Interior integrated with daylight.
SCHOOL OF DESIGN
UNIVERSITY OF PENNSYLVANIA
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ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE OVERCAST SKY - MALDIEVES 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE OVERCAST SKY - MALDIEVES 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY SKY - MALDIEVES
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The movement of sun at Maldives is almost over head. So there are similar sun angles and altitude for other half of year. As a result of which sunlight penetrate at almost similar angle in the room, at early morning and late afternoon and has similar illuminance level inside the space. Not much difference was found in illuminance level with and without light shelf during month of March, for both sunny and overcast sky. As there are no opening on the north facade, there is no much effect found in month of June when sun is in the north. During December, as sun is the south, once can see remarkable effect of difference of illuminance in space with and without light shelf during sunny sky condition. It is important to note that there is not much effect of light shelf during overcast conditions. Other significant result was that illuminance level are almost similar at the end of the space, for both case of with and without light shelf. Also, for the cases with light shelf, there is little increment in the illuminance level at periphery region only near the window.
Interior
ANNUAL SUN MOVEMENT
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21st JUNE SUNNY SKY
STUDY 1 - MALE, HULELY - MALDIVES
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UNIVERSITY OF PENNSYLVANIA
21st JUNE OVERCAST SKY
21st JUNE SUNNY SKY
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ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE OVERCAST SKY - MOSCOW
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ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY SKY - MOSCOW 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0
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Axis Title
The movement of sun at Moscow is from south. Moreover the altitude of sun during December is extremely low. Effective results were found for illuminance level inside space for both the cases, with and without light shelf. Depending on location of light shelf and time, it allowed sunlight penetration accordingly and gave illuminance level accordingly. Here too, as in Maldives, no effect of illuminance level changes occurs in overcast sky. Interesting result were found for December when sun is at the lowest angle and as a result of which there is no effect of light shelf. Sunlight enters the room directly during December and because of that illuminance level increase at the end of the space.
Interior
ANNUAL SUN MOVEMENT
Interior - Exterior
STUDY 2 - MOSCOW, RUSSIA
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ARCHITECTURE 632 006 - DAYLIGHTING
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ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY SKY - MOSCOW
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ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE OVERCAST SKY - MOSCOW
ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY SKY – MOSCOW
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SCHOOL OF DESIGN
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UNIVERSITY OF PENNSYLVANIA
OBSERVATION AND CONCLUSION GENERAL • Light shelves does not work well for places which has major overcast sky conditions throughout year. • Helps well in decreasing the peripheral glare and discomfort • Effect of inside illuminance and reducing peripheral glare and discomfort depends on width of light shelf, location (inside, outside or both), vertical positioning, its angle and also on dimensions and type of glazing. • Depending on the requirement of the space, one can decide upon having light shelf either interior, exterior or both, as they all have different effect on illumination at interior space near perimeter. • Not much effect have been seen at the end of the space using either of 3 cases.
12 PM
9 AM 12 PM 5 PM
JUNE
DECEMBER
SUN MOVEMENT - MOSCOW, RUSSIA
MARCH
9 AM
DECEMBER
5 PM
JUNE
SUN MOVEMENT - MALE - HULELU, MALDIVES
MARCH
MALE - HULELU, MALDIVES
MOSCOW, RUSSIA
• For location near equator, light shelf doesn’t work during months around March and September as sun is almost overhead. • Light shelf works equally well for north and south façade. • Illuminance level is almost similar inside space in the central part during early morning (9AM) and late afternoon (3PM) as sun penetrates the space at almost similar angle from south.
• For location moving far above tropic of cancer, light shelf doesn’t work during months around December as sun is at very low altitude, even during noon time. • Light shelf works well for months between months from March to September as sun is at higher altitude compared to other months.
ARCHITECTURE 632 006 - DAYLIGHTING
SCHOOL OF DESIGN
UNIVERSITY OF PENNSYLVANIA