# Calculating daylight factors

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:

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,
2200 København N
Denmark

mobil: +45 26 39 06 40
E-mail: perhaugaard@yahoo.dk

Trænger du til at se det store billede? Kelkoo giver dig gode tilbud på LCD TV! Se her http://dk.yahoo.com/r/pat/lcd

Hi Per,

Looking at what you are doing with rcalc, it looks like you are assuming a 10,000 lux overcast CIE sky. While this is fine, you do need to tell gensky the output of the desired sky explicitly. To do this you can use the -B switch and provide the horizontal diffuse irradiance. This can be calculated as 10,000/179 = 55.866 w/m^2. With this your gensky line should read:

gensky 6 21 12 -c -a 59.9 -o 10.8 -m -15.00 -B 55.866

With this you should get some different results in your rcalc.

Regards,

-Jack de Valpine

PS: for further reading on this you should take a look at Chapter 6: Daylighting Simulation in /Rendering with Radiance/, this chapter is by John Mardaljevic.

Per Haugaard wrote:

···

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
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
7 0.359 0.359 0.359 0.080 0.000 0.939 0.600

# The window
void glass window_glass
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
4 1 1 1 0

sky_glow source sky
0
4 0 0 1 180

skyfunc glow ground_glow
0
4 1.4 .9 .6 0

ground_glow source ground
0
4 0 0 -1 180

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

ground_mat ring groundplane
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:

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,
2200 København N
Denmark
mobil: +45 26 39 06 40
E-mail: perhaugaard@yahoo.dk

------------------------------------------------------------------------

Trænger du til at se det store billede? Kelkoo giver dig gode tilbud på LCD TV <http://dk.yahoo.com/r/pat/lcd>!

------------------------------------------------------------------------

_______________________________________________