I am trying to model blinds and would appreciate any help possible. I got
some ideas from the desktop radiance manual, however have still not been able
to model them properly.

I am trying to model blinds for the glazing in a simple room with a south
facing glass.
I wrote the genblinds rad file as follows:

and I tried modeling the blinds in the following two ways.

1. here the glass is the illum and the blinds are located towards the
room side next to the glass. (modeled using mkillum, using rad)

2. here I modeled the glass and special illum separately. The special
illum is located towards to inner side of the glass and blinds setup. (modeled
using mkillum, using rad)

Neither of them gave me proper results, i'm sure I was doing something wrong.
The glass and illum were both getting modelled sperately it seems, because the
sun component remained unchanged. What is the correct way to model blinds??

Is there another way of modeling the blinds? I would really appreciate some
help here ...if there is some text I should be reading...let me know.

Thankyou
Amarpreet

Amarpreet Sethi
Graduate Student
Arizona State University

What do you see when you look at the blinds with rview? Are they in the right place? What is the description of your window polygon?

Using mkillum with blinds is a bit tricky, as the most efficient calculation looks at only a small polygon in the middle of the window, then applies the computed distribution to the whole window. There really shoul be a script to do this for you for some common blinds configurations, but I never got around to writing one. Any volunteers?

I don't see how 58.29 is a sensible value for the number of slats.

We carried out an validation study of RADIANCE, comparing measurement and
simulation of an external venetian blind system under over 10000 different
sky conditions (sunny and overcast). The results have been published in:

Reinhart C F, Walkenhorst O, "Dynamic RADIANCE-based daylight simulations
for a full-scale test office with outer venetian blinds." Energy &
Buildings, 33:7 pp. 683-697, 2001.

The results show that RADIANCE can accurately model blinds. The main
difficulties are:
- you have to characterize the surface properties of the blinds with a very
high accuracy
- you have to make sure that the slat angle of the simulated blinds exactly
corresponds to the measured blinds
- for ceiling sensors you have to also carefully model the exterior of your
test room
- you have to set your simulation parameters sufficiently high. We used:
ab 7
ad 1500
as 100
aa 0.1
ar 200
dt 0
ds 0
- we did not use mkillum

Christoph
Christoph "Tito" Reinhart, Ph.D. tel: (613) 993-9703
Research Officer fax: (613) 954-3733
Institute for Research in Construction e-mail: [email protected]
National Research Council Canada 1200 Montreal Road M-24, Ottawa
Ontario K1A 0R6 Canada

What do you see when you look at the blinds with rview? Are they in
the right place? What is the description of your window polygon?

Using mkillum with blinds is a bit tricky, as the most efficient
calculation looks at only a small polygon in the middle of the window,
then applies the computed distribution to the whole window. There
really shoul be a script to do this for you for some common blinds
configurations, but I never got around to writing one. Any volunteers?

I don't see how 58.29 is a sensible value for the number of slats.

Hi Greg,
I wonder if your comment about using mkillum with blinds is true also for a specular horizontal lightshelf placed inside a room at the lower edge of the window? I gess, the calculation accuracy will be higher for lightshelf than for blinds?

Barbara.

···

Using mkillum with blinds is a bit tricky, as the most efficient calculation looks at only a small polygon in the middle of the window, then applies the computed distribution to the whole window. There really shoul be a script to do this for you for some common blinds configurations, but I never got around to writing one. Any volunteers?

I don't see how 58.29 is a sensible value for the number of slats.

You could use a smaller polygon for a light shelf, but there is less benefit from doing so. You get a more efficient calculation in the case of blinds simply because you don't have to compute and place as many ambient values if you restrict mkillum to a smaller area, yet the result (provided there is no nearby exterior geometry) will be just the same.

I am attaching my reply to Amarpreet below for those who are interested.

In the case of your lightshelf, you probably don't need mkillum if the shelf is purely specular (i.e., a mirror), but you should definitely use the "mirror" primitive type for its material and set -vr 1 (or higher).

-Greg

···

From: Barbara Matusiak <[email protected]>
Date: Tue Oct 28, 2003 11:07:09 AM US/Eastern

Hi Greg,
I wonder if your comment about using mkillum with blinds is true also for a specular horizontal lightshelf placed inside a room at the lower edge of the window? I gess, the calculation accuracy will be higher for lightshelf than for blinds?

Barbara.

Using mkillum with blinds is a bit tricky, as the most efficient calculation looks at only a small polygon in the middle of the window, then applies the computed distribution to the whole window. There really shoul be a script to do this for you for some common blinds configurations, but I never got around to writing one. Any volunteers?

I don't see how 58.29 is a sensible value for the number of slats.

It is difficult to tell from your renderings, but iit looks like your illum surface is closer to the window than your blinds are. You need them to be on the other side of the blinds, preferably making (or nearly making) a seal between the blinds and the room. The upper, uncovered portion of the window, should have a separate illum surface or perhaps none at all.

For a more efficient mkillum calculation, create the polygon and place it appropriately as I have described above. Put it in a separate file, as you say you have done already for rad. Then, scale the blinds by a scalefactor 1/N and back, where N is the number of blinds, using the following bit of C-shell code to this file, which I will call "win_illum_poly.rad":

You must substitute the {1/N} and {N} symbols above by the numerical results based on the number of blinds. If you have 11 blinds, these values would be 0.0909091 and 11, for example.

I hope this helps.
-Greg

P.S. I apologize for the delay, but I am in NYC and rather preoccupied with meetings, etc.

From: [email protected]
Date: Sat Oct 25, 2003 10:04:07 PM US/Eastern

Dear Greg,

Thankyou so much for your answer. And I would really like to utilize the idea
of calculating the distribution of a small polygon, as the times for my
simulations are as much as a whole day. However I really am not sure how I do
this.
Right now I am using Rad where I am specifying the scene file with the special
illum material. And then Rad does everything. Hence if I were to do this I
would have to do it without rad. Would I use skyfunc and do it? Would i
create .dat files using skyfunc? and then how would I use the .dat file to do
the rest of the calculation. I am really uncertain how I would do this and
didnt now where to find this information. Hence if you would be able to tell
me how it would be extremely helpful.

Thank you very much for your help, and sorry for asking soooo many questions.