Example: Ray-tracing Evaluation Clerestory Mirror Designs By: Gregers Reimann 20 September 2005

AutoCad based Ray-Tracing Tool Software conceptualized together with CK Tang Software written by CK Tang using the Lisp code, which can be run with AutoCad Software completed 15th September 2005 Excerpt of software code

Analysis of Clerestory Reflector Designs Designs analysed: No outer reflector Parabolic reflector + 1 inner flat mirror (original design) 3 outer flat mirrors + 1 inner flat mirror 3 outer flat mirrors + 2 inner flat mirrors Circular outer mirror + 2 inner flat mirrors Screendump of AutoCad file

Ray-Tracing Input Start angle: 0 deg (horizontal) End angle: 180 deg (horizontal from the other side) Angle step interval: Every 5 deg Number of rays: 40 at each angle step interval Rays evenly stretched along 2.6 meter line pivoted at top of window Pivot point 2.6 m line

Ray-Tracing Software Features 2D ray-tracing analysis Surfaces are either perfectly specular (reflective) or completely non-reflective (i.e. no rays reflected) Rays are reflected 100 times and are not reduced in strength for each reflection Parallel rays from user-defined angle intervals are emitted and the percentage of the rays that reach their desired destination (e.g. from outdoors to indoors) is automatically calculated The ray analysis is automatically put in a text file for easy import and analysis in Excel

Example of Ray-Tracing (with only a few rays) 2.6 m line that is rotated Pivot point Outer reflectors Inner reflec- tors Opening to atrium: 26% of rays reach here

Ray Penetration at Different Angles (0 = horizontal; 90 = vertical)

Relative Ray Penetration

Conclusions The two inner mirrors perform considerably better than the single inner mirror. A split inner mirror design is therefore recommended. The solution giving the highest light penetration is: 3 outer flat mirrors + 2 inner flat mirrors All the solutions with the outer reflector give a high light penetration for steep angles around vertical. This is where the sun often is positioned. The bulkiness of the frames holding the mirrors and grills inside the clerestory opening should be minimised not hinder light entry The internal surface below the clerestory window should be highly reflective (NB. For the simulations it was assumed to be spectrally selective).