The ability to take into account reflections from obstructions is of fundamental importance in building energy simulation (BES), because reflections can have a substantial influence on solar gains. In BES tools, this ability is often implemented duplicating functionalities that have already been solved efficiently in lighting simulation tools. This happens because importing those functionalities from a lighting simulation tool (source) into a BES tool (target) is usualy a complex operation producing non-portable results. This article demonstrates that this ability can be imported modularly and portably without intervening in the internals of the two tools. This can be obtained by: (1) creating, in the source tool, pairs of models which are analogue—on the one hand—to the original model in the target tool, and—on the other hand—to the model in the target tool hypotheticaly enriched with some predictive ability only available in the source tool; (2) measuring, at each time step, the ratio between the performances predicted by the source tool as regards the two analogue models; (3) re-scaling, at each time-step, the performance predicted by the target tool on the basis of that ratio. When appropriate analogue models are utilized, this strategy enables distinct simulation tools to work like an integrated computing unit.