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How to get Useful daylight Illuminance ?

asked 2014-11-23 23:49:53 -0500

hema's avatar

updated 2017-05-04 08:55:11 -0500

I have an idf file which has bsdf data of cfs system. When I run this idf file in energy plus it gives me point in time lux values annually at a point. I want to use these values and calculate useful daylight illuminance. I hope this makes sense?

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@hema Can you edit your question give some more details? What is UDI? What information do your data contain?

Neal Kruis's avatar Neal Kruis  ( 2014-11-24 09:22:13 -0500 )edit

@hema, your file is weather data for a location and I think you're looking to calculate Useful Daylight Illuminance for a particular space in a building? What simulation tool do you want to use? ..

keb's avatar keb  ( 2014-11-24 09:44:44 -0500 )edit

@hema Thanks for taking the time to edit your question. I think it's much more clear, now.

Neal Kruis's avatar Neal Kruis  ( 2014-11-25 08:31:22 -0500 )edit

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answered 2014-11-24 09:50:31 -0500

updated 2014-11-25 14:10:02 -0500

Hi @hema,

OK, so that idf file is giving you daylight illuminace data for all the illuminance maps, which is sounds like you've already gotten out of the eplusout.sql file and into xls, or csv format. Great. At that point, calculating UDI with this is as simple as binning the data into those timesteps that meet the UDI criteria, and those which do not. Originally UDI (Useful Daylight Illuminance) was considered met for the timestep if it was between 100 and 2,000 lux. More recently the upper threshold has been raised to 3,000 lux, owing to the fact that most computer monitors these days are flat (shape) and matte (finish). Therefore, all you need to do is take your data and "score" each timestep depending on whether it meets the UDI criteria or not.

That said, UDI is a so-called dynamic daylight metric, and is really intended to be used in a climate based daylight modeling modality, which implies you have at least hourly data for the entire year.

While OpenStudio calculates UDI on a per-space and a whole-building basis for you if you use Radiance as the daylight simulation tool, the Radiance support does not currently include support for BSDFs. This is in the works, however and will be in the OS GUI this year (and will be usable via a measure even sooner).

BTW this paper is a good resource on the current evolution of UDI as well as its intended use.

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So,i can import idf file in open studio and get the desired results?

hema's avatar hema  ( 2014-11-24 10:05:37 -0500 )edit

Let's clarify what you have, first. You say you "have point in time data (xls file) of an year for a place in India". What does that mean? I ASSumed that was daylight illuminance data for some subset of annual hours. Others are speculating what you have is weather data. Neither of those things is an idf. What you need is a) weather data; b) a building model. These will get you daylighting data. If you have an idf, this could be imported to OpenStudio and you could get UDI that way, yes. You may need to revise your question as Neal suggests, in order to make the answers clearer.

rpg777's avatar rpg777  ( 2014-11-24 10:40:30 -0500 )edit

Also, idf file is having bsdf data. So, openstudio will still be useful?

hema's avatar hema  ( 2014-11-25 04:06:33 -0500 )edit

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Asked: 2014-11-23 23:49:53 -0500

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Last updated: Nov 25 '14