[TRNSYS-users] Why is IB_N = Input9 * LT(AI_N, 90) in the wizard for Building Project, when Inpu9 is the beam radiation from type109

[Alfred Haider]

Hello,

today I got the 16.1 TRNSYS.
I tested the project wizard to build a simple building project.
When finished the data from type109 will go through a Equa called 
"Radiation"
There is a formula I don't understand.
IB_N = Input9 * LT(AI_N,90)

Why is the "beam radiation of titled surface-1" 'North' (input9) 
multiplied with LT(AI_N,90) to get IB_N. I tought "beam radiation of 
titled surface-1" is the IB_N

And why only North. Every other orientation gets simple the data from 
type109 without modification.

Hope someone can help me.

bye,
     Alfred