Design and fabrication of sunlight-redirecting and infrared-insulating microstructure

Abstract

Air-conditioning and artificial lighting consume over 50% of the energy in a building. Decreasing thermal loading and introducing sunlight into a building can effectively save electricity and reduce greenhouse effect. This study reports a design for a passive prismatic sunlight-redirecting microstructure coupled with infrared (IR) insulation. The infrared insulation is an anti-reflection nanostructure with a silver thin film. The base design uses a quadrangular prism with a 45° vertex angle and a height and pitch of 50μm to direct the high intensity sunlight deep into the room; unfortunately, this design produces harmful glare, and the area lighted by the redirected sunlight drifts as the varies sunlight during the day. The prism is further modified using an inclined-curved complex, which has 18.3μm pitch and 20.91μm height. The curved plane can diffuse the sunlight into a wide-angle exiting sunlight beam, which provides uniform sunlight with a stable daylighting area. The experimental results show that the daylighting redirection efficiency reaches 70% at solar elevation angles of 40–70° and that the daylighting area can reach up to 7m deep into the room. The average transmittance is lower than 15.46%, and the reflectance is higher than 75.64% at infrared wavelengths.