Materials definition

Dear all,

I have already done some daylighting simulations now. However, the low
results obtained stroke me and I think that I cannot trust them. I suppose that my definition of materials is not correct. In fact, I am using Google Sketchup and Daysim in order to conduct my simulations. A daysim materials library can be imported in Sketchup. Currently, when I used the typical singleglazclear90 I have this description "void
trans SingGlaz 0 0 7 0.9001 0.9001 0.9001 0.0000 0.0000 0.0909 1.0000".
In order to check if I understood properly the trans definition, I
would like to know if it means that my glazing only transmits about 10%
of light inside my room? I have some difficulties to fully understand the trans definition. Nevertheless, when I try to change the
transmission parameters, the results seems to be too high... If someone could help me to understand, I would be very grateful.

In addition, I have seen that there is another way to define glazing, with the glass definition. What is the difference between these two definitions of materials? What is the simplest way to define a typical single glazing? There may be a library with examples of glazing that I could use?

I would like to thank you in advance.

Kind regards,

Virginie GROSDEMOUGE

Second-year student at ESIROI CODE (Sustainable Construction)
http://esiroi.univ-reunion.fr/
Reunion Island, France

Hi Virginie!

In addition, I have seen that there is another way to define glazing,
with the glass definition. What is the difference between these two
definitions of materials? What is the simplest way to define a typical
single glazing? There may be a library with examples of glazing that I
could use?

The trans material is for translucent materials. Getting its parameters
defined is rather complex and one of the frequently asked questions.

For a typical, clear glazing, glass is the option you should use! It is
an approximation, as not a solid glass volume is considered but the
glass pane is approximated as a zero-thickness pane of given transmissivity.

If you do not have manufacturer data available, download the optics tool
from lbnl, which takes values of the international glazing database
(igdb) to set up your glazing made of glass panes, coatings, air gaps.
This tool will offer an export option to Radiance, which will be a glass
definition for a typical clear glazing.

Cheers, Lars.

Or, if you already know the glass transmission you want to model, you can calculate transmissivity for the material definition from the total visible transmission (Tn in this formula):

From http://radsite.lbl.gov/radiance/refer/ray.html#Materials

  transmissivity = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn

So, if you want a glass of 90% transmission, replacing Tn with 0.9 gives transmissivity of 0.9801, so your radiance material would look like

void glass glass_90percent_transmission
0 0 3 0.9801 0.9801 0.9801

···

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