Accurate modeling of window reveals & mullions

[David_S]

Morning to all,
I am modeling an office building with large façade windows with the intention to verify daylighting levels against the LEED requirements.

The windows are positioned in a wall that is 550mm thick and are split by mullions that are about 250mm deep. The situation is illustrated here: http://postimg.org/image/q6lqvjt03/

What is the best way of modeling this kind of situation in IES VE (i.e. taking accurately shading & reflective properties of reveals, jambs and mullions to account)? More specifically:

1) Modeling window reveals
I have tried two ways:

a) not modeling window reveals specifically, assuming that the software 'sees' the reveals based on the wall thickness (I am using the 'inner volume on'). I guess that in this case, the reveal surface reflectance is equal / set to the exterior wall reflectance?

b) creating window reveals with local shades. While more laborious, my assumption is that this method can give me greater control over the reveal reflective properties, as it can be set for the local shade level (I've verified that this makes an impact on the results, i.e. when the reveal reflective properties are equal to the external wall reflectance, the results are identical to case a), while when the reveal reflectivity value is increased, lux levels slightly increase).

The cases are illustrated here: http://postimg.org/image/uz280ec8h/

Are my assumptions correct? In a case it does not work in this way, how would you go about that?

2) Modeling mullions
The way I have approached modeling mullions is by modeling the whole window as a one pane of glass first, and then used local shade to construct the mullions behind the glass (assumption is that the exterior part of the mullion is too small to play any difference). This is how it looks like: http://postimg.org/image/y04fhco7n/

Again, by comparing the illumination of the room with and without the mullions, I have verified that the mullions are picked by the model (i.e. there is a difference in the result with the trend I would expect - the room with mullions is less illuminated).

Would you use the same / other way of modeling this kind of situation?

Many thanks in advance for sharing your thoughts & experience on my queries

David

PS: For the simulation, I use the Mid/High setting, including the obstructions & reflections from 'Surfaces from shading bodies' option turned on.