DayLight Factor Difference between HONEYBEE and other daylight analysis programs

Replies to This Discussion

Permalink Reply by Elzine Braasch on February 1, 2016 at 3:02pm

Hi David,

I might not be able to fully answer your question as I have no experience with Dialux (my daylighting experience comes from 3DS Max Design). However, the location input, cloudy sky setting and time are all input into the creation of the Standard CIE sky which you use for Daylight Factor calculation. If you are doing a DF calculation, you would require the DF analysis recipe and the Standard CIE sky which has all those inputs which Dialux has.

Hope this helps...

Kind Regards

Elly

Permalink Reply by Theodoros Galanos on February 2, 2016 at 12:11am

Hello David,

DF calculation is not time or day sensitive afaik. From my limited knowledge what you essentially do is calculate the daylight performance of your space under a standard luminance value (which yes can vary from place to place). I am not very convinced with Dialux (at least the version I have tried) because it does not offer any control over the radiance and sky properties, unless I missed smth.

If you provide us with your HB file and perhaps a table comparing the options used in both people in here would be of great help.

Kind regards,

Theodore.

Permalink Reply by David Maimone on February 2, 2016 at 2:12am

Hi All,

thanks a lot for your help.

I post here the difference between Honeybee and Dialux parameters. For Honeybee I can only choose cloudy or uniform CIE sky (no hours, days, months and location). In Dialux all of this information can be set before doing the daylight factor calculation.

Kind regards

David

Attachments:

• Daylight factor honeybee.png, 128 KB
• daylight factor dialux.JPG, 52 KB

Permalink Reply by Theodoros Galanos on February 2, 2016 at 2:36am

Hmm it is strange because I feel that DF calculation involes firing equal luminance beams from all the sky into the model and calculating the lux levels inside. At least that's the impression I have. I don't see how time and date could be relevant as the above is quite time irrelevant in itself. Perhaps I am missing something or perhaps Dialux allows for Climate based simulations (which do get time and date as inputs) without naming them as such?

I'm sorry I can't help more but I'm sure people much more knowledgable than me are on their way :)

Kind regards,

Theodore.

Permalink Reply by Abraham Yezioro on February 2, 2016 at 6:04am

Hi,

The DF definition is:

The design day for daylight factor calculations is based on the standard CIE overcast Sky for 21 September at 12:00pm, and where the Ground Ambient light level is 11921 Lux.

Saying that the DF component in HB set the date to Dec 6 at 12:00 (Mostapha: Is that right? and does it complies with the previous definition?)

For you case, and for comparison you can set the date in Dialux as in HB.

-A.

Permalink Reply by David Maimone on February 2, 2016 at 6:10am

Hi Abraham,

thanks for your help. Do you have the link of the source of this definition?

why in HB is used that specific day ( Dec 6 at 12:00)? I will wait for Mostapha to clarify this aspect

Thanks

David

Permalink Reply by Abraham Yezioro on February 2, 2016 at 6:18am

Embarrassed to say that this is from wikipedia. But check for CIE definitions.

Other definitions i have don't mention the date, but yes the hour (12:00). Since it is a relation between light outside and inside i don't believe it will make a difference changing the date (not the hour). You can try this ...

-A.

Permalink Reply by Mostapha Sadeghipour Roudsari on February 5, 2016 at 10:18pm

Sorry for being late! As mentioned by everyone else DF is the same regardless of the time and or orientation. As you can see in this image overcast/cloudy sky is symmetrical:

Also DF is the result of dividing sky horizontal illuminance to the illuminance that the point receives which means if you change the value of the sky the value of light on the test point will change but the relationship and so the daylight factor stays the same. Here is the source code for the sky that Honeybee uses for DF calculation: https://github.com/mostaphaRoudsari/Honeybee/blob/master/src/Honeyb...

I'm curios to know if changing the date and time in Dialux changes the value of DF. It should not. That would be an interesting study.

Permalink Reply by David Maimone on February 9, 2016 at 9:14am

Thanks Mostapha.

when I will test it in Dialux I will let you know the responce about the possibility of having different values for daylight factor, for different time and day.

kind regards

David