Transmitted shortwave solar radiation is distributed over all surfaces in the zone in a prescribed scale. This scale is an input value which may be dependent on the shape of the zone and the location of the windows, but literature [Liesen 1997] shows that the overall model is not significantly sensitive to this assumption.
[Liesen 1997]: R.J. Liesen, and C.O. Pedersen, "An evaluation of inside surface heat balance models for cooling load calculations," ASHRAE Transactions, vol. 103, no. 2, pp. 485-502, 1997.
epsSw. #1162.