QUESTION:

I would like to be able to run a cumulative insolation analysis only on a certain set of selected surfaces -- is this possible ?

ANSWER:

The ability to choose selected objects for calculations will be available in v5.50 of ECOTECT. In the mean time, just use thermal zones instead.

That is, the cumulative insolation calc. will only be done for objects that exist on thermal zones. so just create a separate zone with only the objects you want to do the calc. for and make all other zones non-thermal.