Optimization And Experimental Study Of Optical Fiber Transmission Daylighting System

Because of flexible installation and healthy and safe light,the sunlight transmission daylighting systems via optical fibers for indoor illumination are concerned widely in building energy efficiency areas.The optical daylighting technology is an emerging indoor lighting technology that can introduce outdoor sunlight into any place where illumination is needed.Polymethylmetacrylate(PMMA)fiber belongs to a kind of plastic optical fiber,which is flexible,low in cost and high in transmission efficiency,and is the most cost-effective among all optical fibers,so it is also the most widely used in the field of daylighting.However,it can only withstand a temperature of 70℃ due to the low melting point of plastic optical fiber.In the process of concentrating,it is often melted because of the high energy flux density of the focused spot.Therefore,thermal control measures are crucial,especially in the case that diameter large concentrators are adopted.But the research at home and abroad is still scarce.To solve this problem,this study developed three measures,infrared light filtering as a hot mirror,flux homogenization and fiber facet polishing,respectively to control thermal load caused by a large lens with a diameter of 1m.The experimental data shows that the hot mirror can reflect infrared light(740-1100nm)efficiently,meanwhile keeping highly transparent for the visible spectrum(400-700nm),which produces the cold incident light.A homogenizer was also designed to obtain a uniform spot through re-arrangement of flux distribution.Analysis based on Monte Carlo rays-tracing method(MCRT)showed that the homogenizer could supply a flat flux distribution of 1500 suns by eliminating the flux peak.Microscopy experiments revealed that fine polish could effectively remove dust off the surface of the PMMA fiber,so to avoid heat spot to protect PMMA fiber.At the same time,this paper also analyzed several factors that may affect the efficiency of fiber in the experiment and draws conclusions.A long time daylighting test demonstrated the feasibility of the large lens with an aperture of 1 m for daylighting via optical fibers,which offered an illumination level of 360 lux on al area of 32m2.In this condition,the lighting efficiency of the system is 11%～13%.The research showed that,as long as there was good thermal load control,it is feasible to adopt large lens to obtain huge flux to promote the performance price ratio of optical fiber daylighting systems.