Innovative daylighting systems for deep-plan commercial buildings

摘要

The use of natural light is very beneficial in office buildings because energy consumption can be reduced, and working conditions can be enhanced, which positively affect workers' health and productivity. However, bringing natural light into deep plan office buildings is not possible with simple windows or skylights, and light transport systems are necessary to bring natural light into the deep cores of buildings. Light transport systems usually need sun-tracking devices to collect natural light that are complicated, expensive and require continual maintenance. Mirrored light pipes coupled with laser cut panels (LCP) are a passive and simpler daylight transport solution and are the focus of this PhD research. The primary aim has been to improve the technology and achieve the most efficient passive solution possible through the interactive use of theoretical modelling, experimental measurements and case studies. ududududududApplications of this technology were investigated in two case studies: 1) as horizontal light pipes for daylight illumination of a high rise building proposal in the tropics; and 2) as vertical light pipes for daylight illumination of a middle-rise deep plan building proposal in a subtropical environment. In both cases, quantitative system performance under best (clear sunny sky) and worst (overcast) case scenarios was undertaken via scale model testing and mathematical modelling. The major conclusion for both case studies was that mirrored light pipe technologies, when coupled with LCP, were effective in introducing sufficient ambient light levels inside buildings and over distances > 20 m from the façade or roof. Average lux levels achieved in the space were 150 to 350 lux for the horizontal light pipes and 50 to 300 lux for vertical light pipes. However, as a passive solution, this technology has two major limitations: 1) the dependence on sun azimuth and elevation angles, which result in variations in illuminance levels during the day and the year; and potentially 2) pipe size, as pipes with a large diameter (e.g. 2 m in diameter for 20 m long pipes) are required for optimal performance, such that the large pipes may limit integration in building design. ududududududTwo other solutions were assessed to circumvent these limitations to the mirrored light pipe technology: 1) a passive collector that concentrate natural light by using a fluorescent panel to reduce the size of the pipe, and 2) an active collector comprising a LCP rotating 360 degrees in a 24 hour cycle to reduce system dependence on sun azimuth and elevation angles. The low light-to-light efficiency of the fluorescent panels made them inappropriate for collecting sufficient amounts of daylight necessary for daylighting of large buildings. In contrast, the rotating LCP is a very simple active system that by rotating constantly at 15 degrees per hour, reduces the deviation angle between the panel orientation and sun azimuth angle, and significantly increased the system performance. The performance was generally better (e.g. 2.5 times better for light collection under low sun elevation angles) than the passive light pipe system with fixed LCP. However, active systems raise other issues in terms of cost-benefit in constructing, operating and maintaining such systems. ududududududPassive mirrored light pipes coupled with LCPs or simple active systems with rotating LCPs have great potential as daylight solutions for deep plan buildings as they can contribute to lowering overall energy consumption, improve workplace health and become an architectural design element. Research is still required on the implementation of the technology into buildings, but the growing trend towards 'green buildings', sustainable design and government regulations or building codes will require more daylighting use in buildings, and will motivate designers to increasingly consider and incorporate such daylighting strategies into future building designs.