1. A computerized method for modular development of industrial process models comprising: collecting a plurality of flowsheets, wherein each flowsheet includes a corresponding one of a plurality of groups of unit models; combining the plurality of flowsheets to create a combined model, wherein each of the plurality of flowsheets maintains its identity in the combined model; directing that a first macro associated with a first flowsheet be run; automatically executing, in response to the directing and prior to run-time processing of the combined model, the first macro and other macros by the same name as the first macro; and displaying a graphical representation of the combined model.