Question-and-Answer Resource for the Building Energy Modeling Community
Get s tarted with the Help page
Ask Your Question

Unrealistic illuminance values

asked 2016-01-26 18:51:43 -0600

BasP gravatar image

updated 2017-05-04 08:49:25 -0600

Currently I'm working on a one zone simulation model in EnergyPlus. The room has one glazed facade, south-east orientated. All other surfaces are assumed adiabatic.

When I look to the illuminance levels at the daylight reference point, these levels stay pretty low. <500 lux during the winter and <1000 lux in summer. I checked my material properties and the 'solar distribution' is set to FullExterior. You can find the .idf file here. Is there something I forgot in my model? Or does anyone know the cause of this?

Kind Regards, Bas

edit retag flag offensive close merge delete

1 Answer

Sort by ยป oldest newest most voted

answered 2016-01-27 11:33:06 -0600

updated 2016-01-28 14:43:28 -0600

Well, what values were you expecting? =) I tried to run your model in OpenStudio but it didn't import properly, and what I don't know about EnergyPlus could fill several volumes, so I can't really do a direct evaluation of your model, at least not right now. The geometry did import, and in looking at it, I see two daylight control points, one of which is pretty well shielded due to its location in the space. Your window has a VLT of 54%, which is throttling the daylight a bit, too. I don't know what weather file you used, nor do I know the run period, but if you had a cloudy climate and didn't sample the whole year, I could see you getting values like you're seeing, possibly. They do seem on the low side, but not out of the question, for certain cases. Again, knowing the climate and run period would help.

Update: Having run your model in OpenStudio, using EnergyPlus and Radiance, I also see very different results. (Posted below, note the scales) I'm going to need some input from the EnergyPlus daylighting people here, assuming such people exist...

image description

image description

edit flag offensive delete link more


Thank you for your comment! I used the IDF editor to make the model, that's probably why it won't run in Open Studio. The weather-file used is the weather file of Amsterdam from the DOE. I expected higher illuminance values, because the same room with a north-west orientation reaches values around 15.000 lux. The run period was one year with a timestep of 6 per hour. It's true that you see two daylight control points, but now I'm talking about the reference point at 1 m from the glazed facade.

BasP gravatar image BasP  ( 2016-01-27 12:01:24 -0600 )edit

@BasP, I was able to import your idf into OpenStudio and assign some missing parameters (schedules, constructions), and the model did run. I am seeing the same values as you are and they do seem low. Further I ran the same model with the OpenStudio Radiance measure, and my results are drastically different (and make more sense). I would re-open this question and see if we get some more responses.

rpg777 gravatar image rpg777  ( 2016-01-28 14:36:26 -0600 )edit

@rpg777 Thanks again for your response. Probably there are some people facing the same problem or know how to handle this!

BasP gravatar image BasP  ( 2016-01-28 14:56:39 -0600 )edit

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer


Question Tools

1 follower


Asked: 2016-01-26 18:51:43 -0600

Seen: 124 times

Last updated: Jan 28 '16