[Radiance-general] Asymmetry in Daylight Factor Results and modification of UDI

[Andrew McNeil]

Hi Amalie,

Increasing the number of samples should get you closer to the symmetry you
expect. The best way to do this is by increasing -ad.  You should also try
reducing ambient interpolation by increasing -ar and/or decreasing -aa.

It is common for beginner (and intermediate, and expert) users to focus on
the -ab parameter, but I find adjusting other ambient parameters is
typically more effective.

Best,
Andy


On Wed, Oct 3, 2012 at 8:28 AM, Guglielmetti, Robert <
Robert.Guglielmetti at nrel.gov> wrote:

> Hi Amalie,
>
> Deviations from point to point are to be expected. Radiance uses
> stochastic sampling, which will result in different "answers" from one run
> to the next. Further, I assume you are using a CIE standard overcast sky
> for your DF calculations? THat is not "symmetrical" either. That sky
> increases in radiance as you increase the altitude from the horizon to the
> zenith. It might help to have more details about your model and your
> results to help diagnose this.
>
> Regarding your UDI question, using the latest version of OpenStudio
> (v0.9.0), you could perform a DGP-based UDI analysis like you are trying to
> do. OpenStudio now reports out DA, cDA, and UDI for each space's
> illuminance map to a .csv file. There is also a glare sensor object now
> that reports DGP(simplified). You could write a Ruby script that takes the
> UDI and DGP values and for each timestep makes an evaluation about the UDI,
> using the DGP value as the trigger for the high end of UDI, instead of 2000
> lux.
>
> The glare sensor also can have one or multiple "glare views", as well; the
> max, min and mean are always reported in the .csv file, allowing you to
> evaluate DGP for a range of views, a la Jacubiec and Reinhart's "adaptive
> zone" idea.  Let me know if you want help writing a script that does what
> you want.
>
> - Rob
>
> ________________________________________
> From: Amalie Momme [amaliemomme at gmail.com]
> Sent: Wednesday, October 03, 2012 7:27 AM
> To: Radiance-general at radiance-online.org
> Subject: [Radiance-general] Asymmetry in Daylight Factor Results and
>  modification of UDI
>
>  Hello all,
>
> I am new to Radiance / Daysim, so I hope you can help help out with a few
> questions.
>
> I am using DAYSIM via Ecotect to simulate the daylight conditions for an
> office, 4 x 5 m, symmetrical geometry, with one window. I noticed that the
> Daylight Factor results were not completely symmetrical. Deviations are
> typically around 0.1-0.3 % DF. I tried increasing the number of ambient
> bounces from 6-8-10 which did not eliminate the asymmetry. I contacted an
> engineer who has been using Daysim via Ecotect in his ph.d. study, and he
> wrote that his Daylight Factors were also a bit asymmetrical. Can anyone
> explain why this is the case? In theory the Daylight Factor should be
> completely symmetrical, as the CIE Standard Sky is symmetrical. Does this
> have anything to do with Daysim using the Daylight Coefficient Method?
>
> Another thing is that I would like to modify the UDI to make it case
> dependent. So instead of using 2000 as the upper limit for useful daylight,
> I would like to insert a sensor point, calculate the DGP (Daylight Glare
> Probability), and use this as the upper limit. Does anyone know if it is
> possible to extract the results for each hour, for each sensor point, to
> count the hours of useful daylight based on this?
>
> Thank you in advance,
> Amalie Momme
>
>
>
>
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