sunny sky and clear sky conditions

All,

I use IES <VE> Radiance among other software to help design teams optimize
daylighting design.

The dilemma is - The same illuminance distribution that's well above the
design fc level under sunny sky conditions is well below that threshold
under standard clear sky. I just double check to make sure it's meeting the
LEED criteria of 75% of space meeting 25 fc at noon on June 21 under clear
sky conditions and it almost never does (I use the standard clear sky in IES
Radiance for that).

What is the difference between the standard clear sky and sunny sky models
within IES Radiance? In the rendered image, I never see solar penetration
into the space under clear sky conditions, what am I missing?

Thanks,

Ramana Koti, LEED AP
Sustainable Building Analyst

ELEMENTS division of BNIM architects
106 W. 14th Street Suite 200
Kansas City, Missouri 64105

p 816.783.1635 f 816.783.1501
www.bnim.com| elements.bnim.com

Hi Koti (or Ramana, which one is the name?)

Maybe sun is not penetrating the space you are considering, but just the floor outside or some near walls, and then it bounches in .. this could be discovered with simple geometric analisys or checking differences with ab 0 ab 1 and and ab 2.

Anyhow, I'm not experienced at all with skies. I just red something.

Lucio

.All,
.
.I use IES <VE> Radiance among other software to help design teams optimize
.daylighting design.
.
.The dilemma is - The same illuminance distribution that's well above the
.design fc level under sunny sky conditions is well below that threshold
.under standard clear sky. I just double check to make sure it's meeting the
.LEED criteria of 75% of space meeting 25 fc at noon on June 21 under clear
.sky conditions and it almost never does (I use the standard clear sky in IES
.Radiance for that).
.
.What is the difference between the standard clear sky and sunny sky models
.within IES Radiance? In the rendered image, I never see solar penetration
.into the space under clear sky conditions, what am I missing?
.
.Thanks,
.
.Ramana Koti, LEED AP
.Sustainable Building Analyst
.
.ELEMENTS division of BNIM architects
.106 W. 14th Street Suite 200
.Kansas City, Missouri 64105
.
.p 816.783.1635 f 816.783.1501
.www.bnim.com| elements.bnim.com
.

.. Caminante no hay
camino, solo se hace
camino al andar ..

          --- o
meglio ---

.. Caminante el
destino no es al
final de el viaje,
pero en todo el
andar ..

All,

I use IES <VE> Radiance among other software to help design teams
optimize daylighting design.

The dilemma is - The same illuminance distribution that's well above
the design fc level under sunny sky conditions is well below that
threshold under standard clear sky. I just double check to make sure
it's meeting the LEED criteria of 75% of space meeting 25 fc at noon
on June 21 under clear sky conditions and it almost never does (I use
the standard clear sky in IES Radiance for that).

IES only bundles a (to my knowledge rather old) version of Radiance. So
I assume that the sky is generated using the 'gensky' program from the
standard distribution.

There you have the basic sky types of

   * sunny (CIE clear day)
   * intermediate
   * cloudy (CIE overcast day)
   * uniform

plus the option to switch the sun off and on for the first to skies.

What is the difference between the standard clear sky and sunny sky
models within IES Radiance?

In plain standard Radiance terms there is not difference between
'sunny sky' and 'clear sky'. You can find out the command used to
create the sky in the sky file that's created by the IES export
to Radiance. In an older version of IES there was an 'obj' folder
that contained all the Radiance scene files. Search for a file with
'.sky' extension or 'gensky' in the content.

In the rendered image, I never see solar penetration into the space
under clear sky conditions, what am I missing?

I would say that the sky model does not include the sun by default.
Makes sense to me because a sun patch would alter your illuminance
levels in the room beyond a point where a simple threshold value
would make sense.

Regards,
Thomas

···

On 14 Feb 2008, at 16:28, Ramana Koti wrote:

The dilemma is - The same illuminance distribution that's well above the
design fc level under sunny sky conditions is well below that threshold
under standard clear sky. I just double check to make sure it's meeting
the LEED criteria of 75% of space meeting 25 fc at noon on June 21 under
clear sky conditions and it almost never does (I use the standard clear
sky in IES Radiance for that).

-The CIE clear sky is a sky model which has no direct sun input (clear sky
in Radiance, without sun). Does your LEED criteria refer to real life
clear sky condition, or the CIE model? Real life clear sky would
correspond to a sunny sky description.

Kind regards,

···

______________________________
Nicolas Roy
VELUX A/S
Strategic Marketing
Daylight Energy and Indoor Climate