Useful strategy in the design of energy-efficient buildings using innovative daylighting systems

This research work has been carried out to utilize daylight more effectively for indoor illumination in an energy efficient building without any compromise on indoor environmental quality; especially the visual comfort on task plane. Two different daylighting systems have been designed and constructed, and a series of tests have been performed to assess their photometric characteristics as well as their performance. A typical system considered has an optic concentrator capable of tracking the sun and making high density fluxes of solar rays. It consists of either dish or funnel shaped concentrators followed by optical fiber cables and diffusers at the end. The design of a dish concentrator (diameter less than 30 cm) is prepared by rotating a simple parabolic profile in compliance with the major physical requirements. This geometrical simplicity has also been applied for the design of a funnel shaped concentrator created by combining two parabolas. When the sunlight is highly focused, it is then redirected and undergoes a number of reflections to enter a light guide for its final transmission to the terminal device. The light reaching the terminal device finally gets consumed by the interior of a building for indoor illumination. The active daylighting system considered in this study offers substantial advantages over conventional solar designs in its fabrication, installation, operation, and utilization of the sun's energy. The proposed daylighting system is durable and suited to economical operation for different schemes of indoor illumination of buildings. Each component of the system could be made from off-the-shelf technology, thus making the generic unit inexpensive to manufacture. Depending on spatial demand or characteristics, the amount of daylight introduced could be controlled without undue difficulties. To assess the photometric characteristics of a daylighting system, goniophtometer and spectrometemr easurementsa re made,w hich provided its luminous intensity distribution and spectral radiance. The spatial distribution of light emerging from the optical cable is examined by monitoring the workplane illuminances for the mock-up spaces in Nottingham (UK) and Jeju (Korea). Six different types of terminal devices (optical lenses, light rod) are also examined experimentally to elicit the most optimal design for use with a daylighting system. Of those tested, the circular shape acrylic rod spreads out the light most widely followed by semi-concave lens whereas the semi-convex lens has shown the smallest light spreading ability. The test results have revealed some distinctive features of the present dishdaylighting system in bringing natural daylight to non-daylit areas or interior spaces too deep for conventional daylighting apertures. Especially, it proved the effectiveness of the system when applied for individualized lighting allowing individual control over the amount of light in space and to suit individual preferences for lighting conditions. Experimental data from measurements are further extended to develop the numerical models with RADIANCE and ECOTECT for theoretical predictions under different situations. The image of luminance ratio maps generated by RADIANCE and the fish-eye photographs of the sky were conducive to realistic assessment of possible glare reduction and uniformity improvement not just for the task plane but also for its surroundings. There were some appreciable changes made in the indoor luminance distribution thanks to our daylighting system. It has clearly demonstrated its functional reliability and usefulness to control brightness and thus promote indoor visual environment