[Radiance-general] Calculating daylight factors

[Per Haugaard]

Dear Radiance Users,

An existing building is being renovated in order to reduce its need for
primary energy and optimize the building envelope for daylight penetration.
I have build a model in Radiance in order to calculate the daylight factors (DF). I am getting some quite hight DF (21% and 32%) 1 meter from the facade which I think are not realistic.

Below is the  model and  data I used to perform the calculation (I am so sorry for the length of this mail):

The dimension of the room are: (w x h x d) 4 x 3 x 16,8 m
Reflectance inside the room are: Walls: 0,7, ceiling: 0,8, floor: 0,3
The dimension of the window are: (w x h) 1,8 x  2,0 m
The window is placed 0,1 m below the ceiling in the middle of the wall facing.  

Some of the date used in Radiance:

# LightShelve  
void trans refl_white
0
0
7  0.0 0.0 0.0 0.950 0.000 0.000 1.000

# Lamella VSG 12/12 60% light gray printing
void trans printed_glass
0
0
7  0.359 0.359 0.359 0.080 0.000 0.939 0.600

# The window
void glass window_glass
0
0
3 .87 .87 .87

# SkiCIE for Olso
gensky 6 21 12 -c -a 59.9 -o 10.8 -m -15.00

# Outside
skyfunc glow sky_glow
0
0
4 1 1 1 0

sky_glow source sky
0
0
4 0 0 1 180

skyfunc glow ground_glow
0
0
4 1.4 .9 .6 0

ground_glow source ground
0
0
4 0 0 -1 180

void plastic ground_mat
0
0
5 .28 .18 .12 0 0

ground_mat ring groundplane
0
0
8
        0       0       -.01
        0       0       1
        0       30

The lamellas are placed perpendicular to the window and the lightshelve is placed 0,5 m below the top of the window. The lamellas are placed on the exterior side of the pane and are used as shading on sunny days. The lightshelves are placed both on the interior and exterior side of the window., hence used as shading and to lead the daylight further into the room.

Hereafter I have initiated: 

oconv SkyCIE.rad outside.rad office.mat office.rad window.rad LightShelve_ret.rad Lamella_ret.rad > DF_OfficeLL.oct

and

rtrace -w -h -I+ -ab 15 -aa 0.2 -ad 512 -as 0 -ar 128 DF_OfficeLL.oct < DFcoordinates.inp | rcalc -e '$1=($1*0.265+$2*0.670+$3*0.065)*179/10000*100'

Do the above defined 'rtrace' and 'rcalc' function take fully account for both interreflections between the lamellas?

Can anybody spot why I get the unrealistically hight DFs (or are they unrealistic?) for the office with (21%) the lightshelve and lamellas and without (32%) these two ad ons.

I appreciate any help :)


Best regards 

Per Haugaard


 ______________________ 
Per Haugaard,
Griffenfeldsgade 33, 2.tv
2200 København N
Denmark
 
mobil:  +45 26 39 06 40
E-mail: perhaugaard at yahoo.dk





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