Finding the horizontal sky illuminace

old forum
1

Hi

I’m trying to find hourly horizontal sky illuminance… I did use the example:

http://hydrashare.github.io/hydra/viewer?owner=mostaphaRoudsari&amp…;

which use DAYSIM to find the daylight autonomy… I looked at the result folder and find internal illuminance, where it started from 0.5 hour?!

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 half the hour …

thanks and appreciate your help


Honeybee_Annual_Daylight_Simulation_Example.gh (506 KB)

2

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

3

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

Honeybee_Annual_Daylight_Simulation_Example_CWM.gh (512 KB)

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Thanks Chris

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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.

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Thanks Mostapha

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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

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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

diffIllum.gh (380 KB)

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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

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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

diffIllum.gh (380 KB)

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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

12

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