While we usually think of building a system model in the Workspace (and, of course, we can have multiple models within a file in different scenarios), you can have multiple, disconnected system models within the work space simultaneously. This has many uses, including facilitating parametric modeling. For example, you're modeling a system with a defined supply flow and want to evaluate the results for various supply flow rates. After building the model, select the whole model (Edit/Select All or ctl+a), then duplicate it (Edit/Duplicate or ctl+d) as many times as desired. For each instance specify a different supply flow and, after running the model, can now compare results for the different supply flows within the same Output window.