[Radiance-general] Calculating daylight factors

[Jack de Valpine]

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:
> 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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-- 
# Jack de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction

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