Data Reliability

[Anonymous]

I'm comparing data generated by the lighting analysis addin (see attached). There's something that I didn't expect. A room on the first level with a window on the north-east main facade has much more light that a seventh level one. Is it possible? Rooms have same shape ,same floor area, same glass properties and same shape and position of the window. Settings are ok and building site obstructions are included in the calculation.

It's strange because,  a first level window sees less sky dome and has a lower radiation than a higher one (as it's shown in Vasari insolation mapping ran at the same hours -attached). Do you have any suggestions? Thank you, 

Marika

[scheerd · Accepted solution]

This is a great question and nice set of test observations.

The one thing I can think of at the moment is that the ower window has more of the neighboring building in it's viewshed, which is very bright at 3pm.  Solar analysis does not take reflected radiation into account, as we don't have spectral information about building exterior surfaces, but lighting analysis does take reflected light into account, as we have visible properties of exterior surfaces.  

To check this, can you remove the neighboring building and rerun the analysis?  Or if you don't mind, you can send the model to me and I'll run some tests.

David

[Anonymous]

I did some tests and I think you are right, refections influence behaviour of daylight through the facade (img -3). In the previous simulation I ran (in the last post) masses had a very high RGB (230-230-230) which was equal to have a 90% reflectivity coefficient.  I've done other two tests: one without masses (as you said - img 1) and another one with a lower reflectivity of neighborhood (RGB 80-80-80 = 20% of reflectivity - img 2). This tests are closer  than before to variations visible in Vasari insolation mapping (where reflections has not been taken into account, similar to have a RGB 0-0-0 (black body). My english is not perfect, I hope I explain myself. 

Thank you, Marika

[Anonymous]

I correct myself: "RGB 50-50-50 = 20% of reflectivity".

[scheerd]

Marika.

Great!  Very clear.  

This isa really a great urban design study and use of the SAR and LAR tools.  Can I ask permission to share your images and the story on our blog?  I also invite you to write a short blog article about your findings that we can post on our Autodesk BPA Blog.

David

[Anonymous]

Yes, of course. You can share them. About the article I'll write it as soon. Where I can send it?

Thanks a lot,

Marika

[scheerd]

Great thanks!

You can send the article in whatever format is easiest for you (Word or something) to me and I'll copy it into the Blog editor wtih any pictures you want to include.

FYI I"m not sure where you are located, but there is an ASHRAE energy modeling conference this fall in Atlanta that is accepting presentations (no paper required) until March 16.  The work you're doing with Solar Analysis and Lighting Analysis is just the sort of thing they're looking for.  If youre interested in submitting something, the link is here:

www.ashrae.org/EMC2015

Thanks again,

David