Calculating daylight factors with OpenStudio?


Hi all,

I just recently started to look into the Radiance/OpenStudio integration, and I am quite impressed by how far it got for CBDM so far. Now, since in project work one may want to start with some basic rules-of-thumb or guidelines before diving into detailed analysis - is there any workaround for the “lack” of daylight factor calculations in the Radiance measures? E.g. can I just start with disabling Radiance as calculation engine, get the daylight factor from EnergyPlus, and at a later point (without modifying my model) continue with Radiance and CBDM?

Cheers, Lars.


Hi Lars,
Sure thing. The Radiance/CBDM thing is just a measure in OpenStudio land, so if you don’t include it in your workflow, EnergyPlus would be used instead (for daylighting). You of course have to have daylighting control objects placed in th emodel in order for EnergyPlus to do the calculation, but once it does, (I think) you can request daylight factors in the E+ output.

I also added DF as an output from the Radiance measure for a client, so another–perhaps better–route would be to make your own version of the Radiance measure that adds DF and optionally skips the full annual simulation – a “pre-design” version, if you will.


Hi Rob,

thank you for confirming this. In fact, the documentation confirms that daylight factors are computed for the CIE sky models, but unfortunately they are not stored.

From the “Output Details and Examples” chapter of the EnergyPlus documentation, I get that EnergyPlus should give me the daylight factors (including those for sky types other than overcast) in a file “eplusout.dfs”. Unfortunately, this file does not show up in my run-folder.

Do you have an idea if I can somehow get the (default) behavior of EnergyPlus to write the daylight factors out to that file?

Cheers, Lars.