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different values for different runs in openstudio

asked 2015-05-18 04:44:23 -0600

eldav gravatar image

updated 2015-07-12 12:06:25 -0600

I have a simple model with an exterior window. I use Radiance for daylighting simulation. I run the baseline model (North orientation) and different WWR (0.1 to 0.9) with PAT. Every time I run the same model, the values that I receive for "zone lights total heating energy" is different for the same model ! For example it changes from 1465 kWh to 1600 kWh for the WWR=0.1. The other strange thing is that in one run for all the cases from 0.1 to 0.9, the value recieved for the WWR=0.3 is more than the case which the WWR=0.2 which it could not be correct but when I run all the cases again, I recieve other values. what is the reason and how can I be sure which results are correct?

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answered 2015-05-18 09:36:07 -0600

Radiance uses a stochastic algorithm to calculate the light transport, which will result in slightly different illuminance values from run to run. The way to get more reliable results is to increase the sampling density -- in terms of number of sampling points and number of rays spawned from each point -- as well as the number of "bounces" followed for the ambient, or global illumination. In OpenStudio under the Radiance Parameters I recommend you select the "Fine" preset, which will increase many of these parameters for you in a coordinated way: image description

These settings should give you more consistent results from run to run, though there will still be some variability in the illuminance results. These results directly inform the lighting load schedule, which presumably directly relates to your Zone Lights Total Heating Energy.

Lastly I have to admit to never having used PAT and Radiance much beyond some simple workflow testing. We'll need to take a look and make sure there isn't some other issue at work here; the strange result in your progressive analysis makes me think perhaps there's something else going on here. Care to share your model? I could take a look.

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In the OpenStudio Application, First I choose "Fine", and then I press the "Run Simulation" button, but when I go back to the Radiance Parameters, the "Coarse" is selected! So, it means that the "Fine" option isn't mentioned in the simulation with Radiance.

How can I send my model?

eldav gravatar image eldav  ( 2015-05-18 13:42:05 -0600 )edit

Sorry, there was a bug in OpenStudio < v1.7.0 where the Radiance parameters would always reset to coarse after leaving that tab. Definitely upgrade to at least version 1.7.0, and while you're at it you should get the latest Radiance as well (here). Generally folks post their models on Dropbox or Google Drive with a link here, to share models and other files for troubleshooting.

rpg777 gravatar image rpg777  ( 2015-05-18 16:38:04 -0600 )edit

I installed OpenStudio-1.7.4.4b995c92df-Win64 and the new version of Radiance. but Now when I run the model in OpenStudio application with radiance, I receive this error: failed to run DaylightSim for annual daylight simulation

with the OS 1.6.3 I didn't have this problem for this model: https://www.dropbox.com/s/9ba1p7n5ssv...

eldav gravatar image eldav  ( 2015-05-26 12:09:07 -0600 )edit

I have installed EnergyPlus 8.3 in the default folder as well but Openstudio found the one that is installed in the share folder where Openstudio is installed. I even added the one that I installed separately but I received the same error

eldav gravatar image eldav  ( 2015-05-26 12:15:45 -0600 )edit

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Asked: 2015-05-18 04:44:23 -0600

Seen: 256 times

Last updated: May 18 '15