01669nas a2200121 4500008004100000245015500041210006900196260001200265300000700277520117000284100001901454856007401473 2011 eng d00aOn the sensitivity of daylight simulations to the resolution of the hemispherical basis used to define bidirectional scattering distribution functions0 asensitivity of daylight simulations to the resolution of the hem c09/2011 a193 a

The Radiance simulation program includes new tools that enable daylight modeling of complex fenestration systems (CFS) using bi-directional transmission distribution functions (BTDF). The tools use the Klems angle basis to define the number of paired incoming and outgoing data values. However, the Klems angle basis was developed for thermal simulations and may be too low of a resolution for some types of daylight systems, particularly those that exhibit peaky, specular transmission. This study evaluates the sensitivity of the angle basis resolution by comparing simulation results for the Klems angle basis against results using two higher resolution angle bases. The first evaluation compares results for specific points in time. The second evaluation compares simulation results using annual performance metrics. Annual lighting energy data were found to agree to within 1%. Annual assessments of discomfort glare were found to disagree by 7% because high resolution basis resolved glare sources into smaller, more intense sources. We concluded that high resolution bases are appropriate for specific types of CFS and performance metrics.

1 aMcNeil, Andrew uhttps://facades.lbl.gov/publications/sensitivity-daylight-simulations