INTRODUCTION:

Nowadays environmental sustainability and conservation of energy are key factors for the building design. Currently the whole world depends on fossil fuels for their major energy requirements [1]. Since the over exploitation of fossil fuels in the last two centuries, present researchers are looking towards renewable energy sources as alternative energy and efficient energy enhancement techniques. Solar energy is a renewable energy in the form of day lighting has been widely used in built environment for reducing energy consumption in artificial lighting [2]. Recent studies revealed that proper day lighting of a building can improve the quality of light in a space and reduce the amount of electrical lighting required. More importantly, daylight provides better psychological benefits to building inmates; this should be a main goal of day lighting rather than the simple reduction of electrical lighting requirements [3]. The day lighting design requires consideration of a range of complex concerns. Our good health is directly associated with receiving optimal levels of quality light. Fluctuating light levels influence even our hormonal levels and biological rhythms. Daylight can have other physiological effects as well[4]. With proper building integration and lighting controls, daylight can significantly reduce the need for artificial lighting. Integration of day lighting strategies with electrical controls can provide automatic adjustments to provide minimum light levels with minimum electricity use. Day lighting should be considered an integral part of sustainable building issues [5]. Before electric lighting, daylight was the primary illumination source for all building types. Increasing the use of day lighting effectively in buildings can offer significant savings in energy consumption. Normally light received may be measured in lumens per square meter or lux, Example, indoor, artificial lighting usually 300-500 lux for offices, outdoors varies from 10 - 30,000 lux. According to Boucher and Fontoynont suggested nearly 50 lux of daylight might provide significant relief from feelings of isolation for people working in dark places like underground chambers[1]. Recent technology made that natural light could be transported by light pipes and optical fibers in a building with little thermal effect. Light pipes were designed to transfer daylight to underground areas[6,7,8]. The Daylight Factor (DF) is a measure of natural daylight in a space. It quantifies the amount of light at a given point in a space relative to the simultaneous amount of daylight available outside [7]. Natural daylight illumination can vary from 5,000 lux in a heavily overcast sky to over 40,000 lux in direct sunlight. This is much greater than that needed for adequate indoor lighting. The Day lighting systems have been classified into two types, Passive Day lighting systems and Active Day lighting systems [9]. The first one is a system of both collecting sunlight using static, non-moving, and non-tracking systems such as Windows, Sliding glass doors, skylights, light tubes, and light Louvers; and reflecting the collected daylight deeper inside with elements such as light shelves. The second one is a system of collecting sunlight using a mechanical device to increase the efficiency of light collection for a given lighting purpose[9]. The Active day lighting systems are further classified as Open loop systems and closed loop system. The earlier one will track the sun without physically following the sun via sensors. These systems typically employ electronic logic which controls device motors or actuators to follow the sun based on a mathematical formula. The later one i.e. Closed loop systems track the sun by relying on a set of lenses or sensors with a limited field of view, directed at the sun, and are fully illuminated by sunlight at all times[10]. This article will mainly focus on Light pipe Design and setup methodologies which has a lot of potential in Day lighting Technologies.

Design of Light pipes :

Light pipes are primarily used for illuminating deep interior spaces where windows does not have provision for illuminating indoor environment. Light pipe consists of mainly three parts (collector, transmission pipe, diffuser) as shown in figure 1. Light pipes, also called sun/solar pipes, solar light, or tubular skylights, are tubes/pipes used for transport and/or distribution of natural light to another location. A light tube uses highly reflective material or plastic optical fiber to lead the light rays through a building. It can also be a prism light guide distributing light uniformly over its length[11].

Fig 1 Composition of Light pipe

Factors which influence the light pipe

A light pipe, provided at roof top which admits light and its primary task is to optimize the transmittance of daylight. It should achieve this without significantly affecting building heating and cooling loads[12]. The major factors which influence the design parameters are as follows.

[i]Reduction in surface condensation. A thermal variation in the light pipe will mitigate temperature differentials, reducing heat exchange and surface condensation. Surface condensation collects on the underside of cold light pipe glazing when warm moist air rises at night. Water stains from minor condensation drips are often mistaken for leaks. The light pipe setup should include a condensation gutter to receive this small amount of water[7, 12].

[ii] Strength and safety. The light pipe opening should be protected from the movement of people on the roof and should resist wear and tear of natural agents.

[iii] Controlling leakages: A flashing and sealed roof surface is the primary defense against light pipe leaks. The same material which is used for Fabricating the curb should be adopted for the roof structure may reduces movement of moisture. Leaks can be further prevented by not puncturing the frame with fasteners. The proper Roofing and Waterproofing techniques should be adopted to arrest the leakages[7, 12].

[iv] Shape and size to enhance efficiency: A light pipe’s shape and size surely influence its efficiency. The designed shapes such as domes and pyramids may capture low angle incident light in the early mornings and late evenings which may be extending the effective hours of day lighting. Normally Flat surfaces may have high reflective angles that may reduce efficiency during the morning and evening hours. The various Photometric reports of light pipe shapes are available for use in developing day lighting designs.

[v] Effective sunlight: To increase efficiency, light pipes need to diffuse sunlight as broadly as possible. Sunlight can be diffused in many ways, such as selecting appropriate glazing material, using diffusing throat materials and appropriate light well geometry, or adding secondary diffusing elements[6,7,12].

Design Components:

Sun pipe is a tubular skylight that collects daylight on the rooftop, then guides it down a highly reflective pipe and diffuses it into the building interior areas. It usually comprises 3 main components[11]:

(a) Dome with curved reflector usually of a clear polycarbonate, capturing daylight on the rooftop. It consists of a light intercepting transfer device so that even daylight is not in the direct path of the tube can also be captured and redirected to interior part of the building. In this way, it increases the daylight collection and harvest for low sun angles, resulting in increased light output as it works efficiently from sunrise to sunset. (b) Pipe consisting of a very high reflective internal finish of aluminum with at least 98% (without special coating) to 99.7% reflectance (with silver coating) and completed with either elbow or straight run, conveying the light beams into the building.

(b) Ceiling diffuser that releases light into the interior space.

parameters for Design

Length:

A light Pipe can be almost any length that you wish, but loses 10% of light for every metre of light pipe. For very long light Pipes, a larger diameter should be used. There is a 16% light reduction for every bend. On smaller sizes the total effective maximum length is 8m, and up to 20m on larger sizes[ 13].

Spacing:

In general terms we recommend 300mm diameter light Pipes at 3 metre intervals, 450mm diameter light Pipes at 4m intervals and 530mm diameter light Pipes at 5 meter spacing’s.

Maintenance:

Due to the shape of the dome, the light Pipe is self-cleaning. The ceiling diffuser fits snugly into the base of the ceiling diffuser to prevent dust or dirt entering the system and as a result the interior mirror finish surface never requires any maintenance. however we are fitting a light kit, the bottom ceiling diffuser can be removed but care must be taken not to leave finger prints on the internal mirror finish of the light Pipe[13].

Wear and tear: The top domes are UV protected and carry a twenty five year guarantee. However, after 10 years there may be a slight clouding of the external surface.

Light pipe Setting works

Outside roof Preparatory Work:

Initially select the area carefully where we want to install our light Pipe. Ensure that there are no obstructions to the installation such as water tanks, pipes, electrical cables, etc. locate exact point of installation where we have to fix the light Pipe to receive the sunlight and where we want it to exit through the roof[14]. Place the flashing plate over the eight pilot holes, aligning the pipe with the holes. Mark the perimeter of the square plate on the roof, and Cut the roof covering back to approximately 50mm beyond the flashing plate. With the help of eight perimeter guide holes, cut a circular hole through the roofing board such that the hole must align with the hole of the ceiling as shown in figure 2. Secure the flashing plate with the help of screws. Provide weatherproofing around the flashing plate with the help of asphalt, lead or felt to a height of 150mm.

Fig.2 Flash plate and weatherproof set-up

Collar fitting:

After the finishing of flashing plate installation and the weatherproof dressing, place the collar over the flashing plate. Drill five equally spaced holes around the collar in the positions and fit the 15mm self tapping screws and washers as shown in figure 3. Develop a weatherproof seal by applying silicone sealant over the screws/washers[14].

Fig .3 Fixing of Collar to flashing plate

Assembling of the pipe:

Place the seam of the pipe on its top and role it. The most important thing is that the protective film should be left on the inside surface of the pipe for the protection of pipe from dust or dirt getting on the surface of the pipe. Align the ends of the pipe with support of special seams clip into one another. Apply pressure on the seam in all directions along its length to ensure the seal is firmly secured as shown in figure 4. Apply a length of aluminum tape over the prepared joint. Maintain a projection of 5 mm for the pipe above the collar and cut approximately 50mm above the room’s ceiling[9,10,14].

Fixing of first pipe:

Place the topmost pipe into the flashing plate from the bottom and allow the pipe to project 5mm through the top of the collar. Secure the pipe firmly in position using self tapping screws and washers. Once the pipe is fixed in position, then apply a thick bead of silicone sealant, to seal between the light Pipe and the collar as shown in figure 5. This is the important part of the light Pipe installation because the silicone sealant will prevent any rain or condensation water stain on the ceiling[9,10, 14].

Fig.5 Pipe fixing on to flashing plate

Fixing of Dome:

Before installing the top dome to the collar, remove the protective film from the top of the first pipe and push it down to form a protective ‘plug’ in the pipe as shown in figure 6. Firmly fix the roof dome to the collar by using the 15mm self tapping screws and washers and ensure that the dome is free from any finger prints, dust or dirt.

Fig.6. Top Dome installation

Fixing of Ceiling Diffuser:

The bottom of the light Pipe should be trimmed back so that it is approximately 50mm above the top of the ceiling. Insert a 3mm plywood backing panel in the ceiling space over the hole to provide extra support to the ceiling diffuser. Now the fixing ring can be screwed into the ceiling and then the bell end can be positioned over the bottom of the light pipe[9, 10, 14]. The ceiling diffuser should be designed to be suitably fit into the bottom of the fixing ring. Ensure by twist the buttons for firm fixing of diffuser in place. If the ceiling is not perfectly flat, apply a thin bead of a sealant around the external edge of the trim to seal any gap between the ceiling trim and of the ceiling as shown in figure 7.

Fig.7 Arrangement of Diffuser

Maintenance:

The light Pipe is designed to be almost self maintenance such that the shape of the dome and the flashing is designed to be self-cleaning. However further cleaning can be done with the help of warm and soap water to wash the external dome and flashing. Ensure that there should not be any scratch the dome when washing. Internal cleaning should not be required since all components are effectively fixed. The Light Pipe can assure a 20 to 25 year of guarantee against any defects arising for faulty materials[9,10].

Advantages of light pipe:

Light pipes avoids the over illumination since direct sunlight is not preferred at most of places. It minimizes the various ill effects caused by the over illumination. Since it uses naturally available solar light and hence there is no ill effect on people. Light pipe utilizes a non-conventional source of energy that means It is an eco-friendly means of illumination. The light pipe can achieve a minimum daylight factor of 2 % in 75 percent of all space occupied[9,10]. It can also provide automatic dimming controls or accessible manual lighting controls, and appropriate glare control. At least 75% of electricity costs can be saved during the daytime, where light Pipes are used to replace the need for electric lighting during day hours. This method is comparatively cheaper with a payback period of about three to five years and it helps in minimizing the light pollution. When combined with proper lighting controls, light pipes can help to save cooling energy by reducing the need to remove heat from electric lighting. The light pipe can reduce the energy usage by 30 percent as compared to the standard building performance rating per ASHRAE Standard.

CONCLUSION:

Light pipe system has wide range of application in the field of sustainable management. It represents modern way of illumination of internal parts in buildings. These pipes can be installed together with artificial lighting for better luminance when day lighting is not sufficient. Even though the initial cost of light pipe is not attractive for the present demand of energy, it may be an alternative in future with better improvised designs. Efficiency of light pipe in buildings depends on many factors such as optical properties of light transmittance of the dome, ceiling diffuser, reflectance of inner surface and dimensions of the light pipe plays an important role. As compared with conventional skylight, the light pipe system can provide more stable and uniform light to the interior of the building sites. Light pipes are efficiently provide pure natural light and also effectively minimizing heat gain and heat loss due to its sealed system. The wider application of light pipes in buildings could also bring positive environmental impact in reduction of Green house gases.

REFERENCES:

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2. V.H.C. Crisp, P.J. Littlefair, I. Cooper, G. McKennan, Daylighting as a passive solar energy option: and assessment of its potential in non-domestic buildings, Report BR129, BRE, Garston, UK, 1988.

3. P.J. Littlefair, Designing Buildings with Innovative Daylighting, Construction Research Communications Ltd., 1996.

4. W. Pohl, C. Anslem, Natural room illumination using sunlight, in: Proceedings of World Renewable Energy Congress VII (WREC 2002), Cologne, Germany, 2002.

5. G. Sweitzer, Three advanced daylighting technologies for offices, Energy 8 (2) (1993) 107–114.

6. G. Enedir, A.T. John, Evaluating the potential for energy savings on lighting by integrating fibre optics in buildings, Building and Environment 41 (2006) 1611–1621.

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9. M. Schiler, Simplified Design of Building Lighting, John Wiley, 1992.

10. D.M. Egam, Concepts in Architectural Lighting, McGraw Hill, 1983.

11. P. Muralidhar, and V Srihari. “Light Pipe – A Sustainable Technology For Better Lighting In Building Services”, NICMAR, Journal of Construction Management, April-June 2015, Vol. XXX(2) pp: 51-56.

12. D.J. Carter, Developments in tubular daylight guidance systems, Building Research & Information 32 (3) (2004) 220–234.

13. V. Garcia-Hansen, I. Edmonds, Natural illumination of deep-plan office buildings: light pipe strategies, in: Proceedings of ISES Solar World Congress, Gothenburg, Sweden, 2003.

14. Monodraught, Sunpipe information leaflet, Monodraught Ltd., 2008.

Received on 16.11.2015 Accepted on 20.12.2015

Int. J. Tech. 5(2): July-Dec., 2015; Page 209-214

DOI: 10.5958/2231-3915.2015.00029.2