Asymmetry in Daylight Factor Results and modification of UDI

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 [[email protected]]
Sent: Wednesday, October 03, 2012 7:27 AM
To: [email protected]
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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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 < [email protected]> 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 [[email protected]]
Sent: Wednesday, October 03, 2012 7:27 AM
To: [email protected]
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

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

Hi Rob and Andy,
Thank you very much for your quick answers!
@Rob: My model is a square office (A box), room depth 5 m, facade length 4
m and height 3 m. It has a window with height 1.8 m, length 2.8 m placed in
the center of the facade, with the bottom 0.9 m above the floor. The
analysis grid is placed 0.9 m above the floor parallel to the xy plane. The
location is Copenhagen, Denmark. So far, there are no exterior obstructions
in the model, but there will be in the final model as the office is in an
urban environment. When I noticed the asymmetrical DF results I thought I
might have done something wrong when building up the model, and I wanted to
fix this before creating a more complex one. The asymmetry is along the
center axis of the room, but if you say this is to be expected due to the
stochastic sampling, then I will accept the deviations and try to decrease
them by playing with the other simulation parameters Andy suggested. Thank
you for your offer regarding help with the script for OpenStudio, that is
very kind of you! However, I think I will stick to Ecotect/Daysim, and skip
the modification of the UDI for now as my experience with OpenStudio is
very limited and I have a deadline. I might return to this later for
fun though.

@Andy: Thank you very much, I will try playing with the other
parameters. (And post future Daysim questions on the Daysim mailing list
:-))

Amalie