finding the horizontal sky illuminace

Replies to This Discussion

Permalink Reply by Khalid Al on December 15, 2015 at 12:12pm

My question: is there is a way to find the horizontal sky illuminance

and is it possible to have the internal illuminance estimated on the hour and NOT the half the hour ..

thanks and appreciate your help

Permalink Reply by Chris Mackey on December 16, 2015 at 8:14pm

Khalid,

You can read in the illuminance values for a given hour using the "Read Hourly Results for an Annual Daylight Study" component like the image below and in the attached GH file:

Depending on your goal, you might also find the "Read DS Result for a Point" component and the "Read All the Hourly Results from Annual Daylight Study" component helpful (man, all of these daylight result components have really long names!)

From my limited understanding of Daysim, I don't think that it can compute the daylight results at a timestep that is less than one hour.  I am fairly certain that the values in the csv file are given on the half-hour because the interpolation between the hours in the weather file gives a more accurate result over the whole year (without east-west bias). I know that this is why I had to do some interpolation between hours for this rough Annual Sun Exposure (ASE) calculation with the sunpath:

http://hydrashare.github.io/hydra/viewer?owner=chriswmackey&for...

The other members on the forum who have a better knowledge of Daysim might be able to give a better answer than I but it seems reasonable to take the HOY that you input into the "Read Hourly Results for an Annual Daylight Study" component as the results for that hour of the study if it would help with your sanity regarding the large data structure.

-Chris

Attachments:

• Honeybee_Annual_Daylight_Simulation_Example_CWM.gh, 512 KB

Permalink Reply by Khalid Al on December 17, 2015 at 4:33am

Thanks Chris

Permalink Reply by Mostapha Sadeghipour Roudsari on December 21, 2015 at 9:44am

Hi Khalid and chris,

If you're interested in the horizontal sky illuminance you can set a test point with no obstruction and then use "Read All the Hourly Results from Annual Daylight Study" to read the results.

Chris is correct about why values are calculated at .5 hour and not the start of the hour. The timestep is still hourly though.

Finally, Daysim is capable of generating the results for timesteps less than an hour (http://daysim.ning.com/page/daysim-subprogram-ds-shortterm-1). We are not currently exposing it in Honeybee though.

Permalink Reply by Khalid Al on December 22, 2015 at 1:23pm

Thanks Mostapha

Permalink Reply by Khalid Al on December 27, 2015 at 5:20am

Thanks again Chris and Mostapha .. I did look at data obtained through "Read All the Hourly Results from Annual Daylight Study". It gives  global illuminance and not diffuse illuminance (sky illuminance) when finding external illuminance under unobstructed sky  .... what I'm looking for is a way to find the diffuse horizontal illuminance (sky illuminance) under un obstructed sky

Thanks

Permalink Reply by Chris Mackey on December 30, 2015 at 9:02pm

Khalid,

If all that you need is the diffuse horizontal illuminance under an unobstructed sky, you can find the data in the epw file like so:

Let me know if I am understanding that is all that you need.

-Chris

Attachments:

• diffIllum.gh, 380 KB

Permalink Reply by Khalid Al on December 31, 2015 at 1:29am

Thanks Chris .... I just want to link DAYSIM internal illuminance with external horizontal diffuse illuminance . DAYSIM results seems to be on half the hour( 7:30, 8:30, 9:30  ..). However, weather file data is not ( data is give on the hour: 7:00, 8:00, 9:00 ...) and DAYSIM seems that it dose not calculate external horizontal diffuse illuminance.

Thanks

Permalink Reply by Chris Mackey on January 2, 2016 at 3:59pm

Khalid,

You can use the native GH math components to interpolate between the hours to get values on the half-hour like so:

I attached the GH file that shows you how to do this.  This interpolation is also what I am doing in this example file where I calculate ASE on the half-hour:

http://hydrashare.github.io/hydra/viewer?owner=chriswmackey&for...

-Chris

Attachments:

• diffIllum.gh, 380 KB

Permalink Reply by Chris Mackey on January 7, 2016 at 12:10pm

Khalid,

Since Mostapha just added a feature to the example file platform, I can show you exactly what I mean in the example file:

http://hydrashare.github.io/hydra/viewer?owner=chriswmackey&for...

-Chris

Permalink Reply by Khalid Al on January 7, 2016 at 12:59pm

Thanks Chris....

just a small note about the results of the file you send, the diffuse sky illuminance seems to give a very large illuminance values. Sky illuminance is usually less than 20000 lux for most of the climatic conditions and regions.

Thanks again