An alternative approach - why not try ESP-r. It is open source and it supports
explicit surfaces floating within a room - such surfaces take part in the solar insolation
analysis, viewfactors can be computed which include them, heat transfer coefficients
can be set (but most people do not bother) and there is a full energy balance
at such surfaces and you can find out how much solar is absorbed on such
surfaces. And ESP-r tracks solar leaving the room as well as entering. ;You can
also overload ESP-r's solar obstructions to act as visual placeholders for
internal objects for visual clues and export to Radiance.
The interface has shortcuts for defining simple internal pairs of surfaces but
they can also be polygons of arbitrary complexity or extrusions from polygons.
I include internal explicit surfaces in many models, especially for office buildings
to represent thermal clutter and to give visable clues
to clients. Thermal clutter
can have a substantial impact on the response times for heating and cooling
as well as giving better information for local comfort studies. Some groups
now include internal thermal clutter in their models as a default approach.
ESP-r models can also be directly exported to Radiance if you want higher
resolution data.
Regards, Jon Hand