Dear All,
I am doing Radiance simulations in atrium well with higher surface reflectances ( 0.6 ~ 0.8 ~ 1, diffuse surface).
But according to "Aizlewood M, Butt J, Isaac K & Littlefair P. Daylight in atria: a comparison of measurement, theory and simulation: Proceedings Lux Europa. Amsterdam, 1997." and "Littlefair P. Daylight prediction in atrium buildings. Solar Energy, 2002; 73: 105-109.", Radiance underestimated the reflected light (Internal reflected component) in atria with high reflectance (some measurements in the paper used a reflectance 0.85 and got the biggest discrepancy in IRC was 4.87). My some simulations got the similar results: simulations underestimated the measurement with reflectance 0.6 and 0.8 and the higher of surface reflectance the bigger is the discrepancy. All the studies used overcast sky model and set a higher ambient parameter setting.
Could you help me explain the divergence from high reflectance simulation using Radiance. Also, if these demonstrate Radiance simulation could bring some bigger errors to the dayligthing simulation in high reflectance environment?
BTW, I will appreciate it very much if you could share some experience or knowledge and give some suggestion about higher reflectance simulations.
Cheers
Jiangtao
PhD student in University of Sheffield
The higher the surface reflectances, the more bounces you need to compute. In pathological cases where you have all white surfaces facing each other in a closed environment, you may need to disable the ambient cache (-aa 0) and rely on Russian roulette sampling (-lr -20 or so). To get a large -ab setting to work (-ab 20 or whatever), you will also need to decrease the -ad setting to make this tractable (-ad 64 or so with -as 0).
-Greg
ยทยทยท
From: Jiangtao Du <[email protected]>
Date: November 8, 2008 9:45:48 AM PST
Dear All,
I am doing Radiance simulations in atrium well with higher surface reflectances ( 0.6 ~ 0.8 ~ 1, diffuse surface).
But according to "Aizlewood M, Butt J, Isaac K & Littlefair P. Daylight in atria: a comparison of measurement, theory and simulation: Proceedings Lux Europa. Amsterdam, 1997." and "Littlefair P. Daylight prediction in atrium buildings. Solar Energy, 2002; 73: 105-109.", Radiance underestimated the reflected light (Internal reflected component) in atria with high reflectance (some measurements in the paper used a reflectance 0.85 and got the biggest discrepancy in IRC was 4.87). My some simulations got the similar results: simulations underestimated the measurement with reflectance 0.6 and 0.8 and the higher of surface reflectance the bigger is the discrepancy. All the studies used overcast sky model and set a higher ambient parameter setting.
Could you help me explain the divergence from high reflectance simulation using Radiance. Also, if these demonstrate Radiance simulation could bring some bigger errors to the dayligthing simulation in high reflectance environment?
BTW, I will appreciate it very much if you could share some experience or knowledge and give some suggestion about higher reflectance simulations.
Cheers
Jiangtao
PhD student in University of Sheffield