Use of Lighting information on EPW file

radiance-general
1

Dear List, I am not sure this is directly applied to Radiance, but for lighting it definitively is.

I was checking out some stuff, and started wondering why are we not using the Lighting information… I am reading THIS, and it says "Illuminance (Global Horizontal, Direct Normal, Diffuse Horizontal, Zenith Luminance).

My question is: Is there any reason for not using the Direct Normal and the Diffuse Horizontal information for making calculations instead of using the Perez Model?

I understand that the Daylight Coefficients would not directly apply since the luminance distribution would be unknown… Is it too bad to consider the direct illuminance as it is, and assume the diffuse illuminance as isotropic (i.e. assume the diffuse daylight entering through my window is the same as the horizontal) ???

THANKS

Germán Molina

2

Dear List, I am not sure this is directly applied to Radiance, but for
lighting it definitively is.

I was checking out some stuff, and started wondering why are we not using
the Lighting information… I am reading
THIS<http://apps1.eere.energy.gov/buildings/energyplus/pdfs/weatherdatainformation.pdf>,
and it says "Illuminance (Global Horizontal, Direct Normal, Diffuse
Horizontal, Zenith Luminance).

My question is: Is there any reason for not using the Direct Normal and the
Diffuse Horizontal information for making calculations instead of using the
Perez Model?

I understand that the Daylight Coefficients would not directly apply since
the luminance distribution would be unknown… Is it too bad to consider the
direct illuminance as it is, and assume the diffuse illuminance as
isotropic (i.e. assume the diffuse daylight entering through my window is
the same as the horizontal) ???

THANKS

Germán Molina

3

Hi German!

Is it too bad to consider the direct illuminance as it is, and assume the diffuse illuminance as isotropic (i.e. assume the diffuse daylight entering through my window is the same as the horizontal) ???

Yes, that would be very bad. There is no such thing as an uniform sky in nature.

Maybe John's chapter on sky model is interesting for you: http://www.iesd.dmu.ac.uk/~jm/doku.php?id=resources:thesis

Cheers, Lars.

4

Ok, I was wondering since I understand this is done commonly in Solar
Energy?

THANKS FOR THE INFORMATION LARS

German

···

2013/8/6 Lars O. Grobe <[email protected]>

Hi German!

  Is it too bad to consider the direct illuminance as it is, and assume
the diffuse illuminance as isotropic (i.e. assume the diffuse daylight
entering through my window is the same as the horizontal) ???

Yes, that would be very bad. There is no such thing as an uniform sky in
nature.

Maybe John's chapter on sky model is interesting for you:
http://www.iesd.dmu.ac.uk/~jm/doku.php?id=resources:thesis

Cheers, Lars.

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