Development of a fiber daylighting system based on a small scale linear Fresnel reflector: Theoretical elements

This paper describes the details of the design of a small scale linear Fresnel reflector (SSLFR) applied to a daylighting system based on optical fiber bundles (OFBs). This study shows the influence of the SSLFR design parameters (mirror width, mirror length, reflector cavity height, and number of mirrors) and the parameters of the optical fiber. A new reflector cavity is designed, consisting of two right trapeziums. Each trapezium collects the incident solar irradiance of the mirrors located at each side of the central mirror. The reflector cavity has two focal points, located in the middle of the aperture of each trapezium. A MATLAB code was developed in order to obtain the optical efficiency of the new reflector cavity and numerical simulations are presented. Two SSLFR configurations, C1 and C2, are studied. C1 is the configuration used in large-scale LFRs and does not consider lateral movement of the OFBs, as is the case in configuration C2. Each of these configurations is analyzed considering the optimal length and longitudinal position of the OFB. Numerical simulations are presented for both configurations using the MATLAB environment. Power consumption based calculations are carried out using the lumen method and the potential electric energy saving is evaluated. The illumination levels obtained are then compared using the lighting design software DIAlux, a free software widely used as a planning tool by lighting designers. The results show a considerable electric energy saving with configuration C2, although configuration C1 also presents good energy savings.