IES LEED v4 - Daylight results inconsistent

asked 2017-08-25 09:47:14 -0500

JohannesBk's avatar

updated 2017-08-25 11:04:38 -0500

I am performing a daylight simulation for an office building (193 000 ft2). I am using the daylight simulation within the IES LEEDv4 navigator (daylight credit option 2). The simulation progress after 40 h was only 65% (150 regular occupied zones). So I tried to perform the daylight simulation for every floor. In this case the simulation has been completed. However, the results seem not to be consistent.

I compared the results of two meeting rooms (level 4 and 5). Both rooms have the exact same orientation, size, window area and window construction (Tvis = 0.71). But the results are completely different for the average daylight 3 pm lux. As a result, 04_Meeting_4_122 meets the requirements and 05_Meeting_4_122 does not. I did not model any trees adjacent buildings.

Average daylight 3 pm lux results:

04_Meeting_4_122: 2176.563 lux

05_Meeting_4_122: 119.877 lux

You can find screenshots of the ies daylight report and a 3d image of the meeting room location via the following link:

Has anyone already encountered similar issues?

Version: VE 2017 0.1.0

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Did you ever find an explanation for this? I suspect distance from the ground would have an effect, as lower levels would have more reflected light from the ground, but this should be a pretty tiny difference, nothing like what you are seeing. Did you also check the solar gain values after a suncast/apache simulation to see if there are similar differences?

bbrannon4's avatar bbrannon4  ( 2017-12-12 21:18:12 -0500 )edit

I have been experiencing similar issues with inconsistency in daylight calculations within the VE. It's been happening much more frequently in recent months. When I run the LEED v4 daylight navigator sim, random rooms will show as having no or very little daylight, and identical adjacent rooms will look normal. It seems that there are failures when Radiance is called for certain rooms and simulation times (since it runs 4 and combines the results after). I've been feeding all the info I can to IES support, and trying to find a workaround in the meantime.Sometimes running the rooms again works.

Greg Collins's avatar Greg Collins  ( 2018-03-15 16:46:12 -0500 )edit

Short update on my issue above. I exported the geometry, created a new IES project and the simulation delivered correct results. Since the update to VE feature pack 3, I have not encountered the issues described above. Greg, I am interested in the answer of the support team.

JohannesBk's avatar JohannesBk  ( 2018-03-20 03:41:31 -0500 )edit