I am trying to understand why there is a significant difference in sDA result (LEED v4 metrics) when using DIVA v4 for Rhino and DIVA v4 for Grasshopper. I am testing this on a sample box. The sDA results using DIVA toolbar gives 36.4% sDA and 38% ASE and when using DIVA for Grasshopper, it gives 77.5% sDA and 37.5% ASE. I tried to to keep the radiance parameters the same for the key variables (ab 6 -ad 1000 -as 20 -ar 300 -aa 0.1).
Attached are the two rhino files along with the grasshopper file. The grasshopper file “Test1.gh”is associated with “Testboxv8v2.3dm”.
1) What is the purpose of “LEEDv4” option under the “Daylight” and the “Grid Viewer” components and how to connect the output to read/view data (See screen shots below). I am getting empty variable when connecting to a panel.
2) Under “Grid Viewer” is there a way to get sDA show up in the rhino interface , currently it appears to be not available as an option for selections under “Grid Viewer” (see screen shot below)
Thank you for your time and feedback.
Apologies for the slow reply. The main reason for the discrepancy is that you haven't set up a shading control for your window in Grasshopper. The 78% sDA is what you would get in the absence of blinds, so it is artificially high.
See the example file "C:\DIVA\ExampleFiles\Grasshopper\Daylight\02_AnnualDaylight_C_WindowsAndShades.gh" to understand how window shades work in Grasshopper.
If you are calculating sDA for LEED compliance, the IES LM-83 standard recommends that blinds be closed whenever >2% of sensor points are exposed to direct sunlight. The Rhino toolbar follows this recommendation automatically when you run the "LEED v4 sDA + ASE" metric. In Grasshopper, however, you need to tell the components what to do. It's actually somewhat tricky to prescribe this behavior, so I'm attaching a GH definition that shows you how to do it. The gist is, you should:
If you set up the control in this fashion, you will get an sDA of 34.5%. The reason it doesn't perfectly match the Rhino result (36.4%) is that the Rhino toolbar uses a non-physical approximation of the fraction of light transmitted when the shade is down, whereas Grasshopper simulates the shade explicitly using Radiance.
If the sDA calculation is not for compliance, but merely for understanding the performance of the space, I would suggest ignoring the LM-83 recommendation and using the Grasshopper components as illustrated in the "WindowsAndShades" example file. This will produce a more realistic shading schedule. In fact, the 2%-area guideline is quite illogical. (Thought experiment: as a side-lit office gets deeper, the shades are closed... less often?)
As for your other questions:
1) LEED credits are awarded if ASE <= 10% AND sDA >= 55% (1 point) or 75% (2 points).
2) No, the Grid Viewer only displays per-sensor values in the Rhino viewport (like DA)
Many thanks for this very useful post. I was diving more into the ASE and checked it for a All-Time shades down with opaque shades. I know it's unrealistic, but I just wanted to calibrate the ASE.
As a result, I get 0% sDA (as expected), but 40% ASE. For the simulation I modified your settings. Please see attached.
What do you think?
Yeah ASE by definition ignores dynamic shading elements (per IES LM-83).
Thank you very much.