[Radiance-general] 3pm to calculate indoor solar transmission

[Bruno Bueno]

Hello,

I'm using the three-phase method to calculate indoor illuminance, and it 
works fine. However, when I use it to calculate total solar transmission 
(irradiance) in a room, I get an underprediction of around 30% (compared 
to other methods such as EnergyPlus). Can anybody tell me what I'm doing 
wrong?

- I have an office with three south-oriented windows. Each window has 
only double-pane glazing.
- I use the -O 1 option in gendaylit to get radiance integrated over the 
solar range.
- I use the solar properties of my fenestration system instead of the 
visible ones to calculate BSDF data.
- I calculate solar transmission by creating two grids of sensors 1mm 
away from the windows (1000 sensors for 4 m2 window area), one facing to 
the windows (front) and another one in the opposite direction (back). 
The total solar transmission in [W] is the irradiance of the "front" 
sensors minus the irradiance of the "back" sensors multiplied by the 
window area.

The three-phase method matrices are calculated as:

Sky vector
gendaylit %i %i %1.1f -a %f -o %f -m %f -W %f %f -O 1 -w -l %i 
|genskyvec -m 4 -c 1 1 1 > daylight/tempSol.skv (%* are replaced by 
actual numbers)

View matrix
rcontrib -f klems_int.cal -bn Nkbins -fo -o daylight/irrSurfFront_%s.vmx 
-b kbinS -m window_south -I+ -ab 12 -ad 50000 -lw 2e-5 daylight/vmx.oct 
< daylight/intSurfFrontSensor.pts

Daylight matrix
genklemsamp -vd 0 -1 0 daylight/SouthWindow.rad | rcontrib -c 1000 -e 
MF:4 -f reinhart.cal -b rbin -bn Nrbins -m sky_glow daylight/dmx.oct > 
daylight/south.dmx

Then, for the "front" grid, I'd just multiply the matrices as:

rlam '!dctimestep daylight/irrWinFront_window_south.vmx 
daylight/tmxs%i.xml daylight/south.dmx daylight/tempSol.skv' | rcalc -e 
'$1=($1+$4+$7+$10+$13)*0.333+($2+$5+$8+$11+$14)*0.333+($3+$6+$9+$12+$15)*0.333'

Similarly for the "back" grid.

Thank you in advance for your help!

Bruno

-- 
Dr.-Ing. Bruno Bueno
Solar Facades
Division Thermal Systems and Buildings
Fraunhofer Institute for Solar Energy Systems ISE
Heidenhofstr. 2, 79110 Freiburg, Germany
Phone: +49(0)761 4588 5377
bruno.bueno at ise.fraunhofer.de
www.ise.fraunhofer.de