Energy-efficient daylight devices

Daylight technology so far has received little attention in planning processes, despite the latest DIN EN recommendations. Quality characteristics of a design that take into account the reduced need for artificial lighting, are barely considered by any certification system like DGNB, LEED or BREEAM. None of the certification systems rewards daylight systems designed to redirect daylight to improve the room illumination and thereby saving electric lighting. The goal of the developments is to achieve daylight autonomy without overheating the buildings. The DIN sets guidelines for reducing the energy transmission in favour of cooling load reduction, but without simultaneously evaluating the required daylighting and visual transmission. Large glass facades are usually planned with darker sun protection glasses in Germany mostly in combination with exterior shading and interior glare protection to prevent buildings from overheating. The energy transmission is indeed reduced to a minimum, however, the lights must be lit to meet the lighting requirements, even when excessive daylight is available outside. The electric lighting, forces the power consumption, and additionally increases the internal cooling loads. The paper will focus on daylight devices based on mirror optics and the light distribution characteristics as well as the g-values simultaneously achieved. The presentation will show different approaches in façade design by discussing finished high-rise projects implementing the latest daylight devices. Measurements concerning the energy consumption for lighting, heating and artificial illumination will be presented. The following paper is an abstract of the book “Daylight Modulation – Strategies for Adaptive Facades” (KOESTER 2015).