Virtual walls can be used should you wish to divide a room into several separate areas (which eventualy creates a scope for heat transfer), for instance if you wish to zone specific parts of a large open plan space individually.
To enter a virtual wall, click on the Add Wall icon below, then select the room in question, and add the wall.
For example, after adding a wall to divide room 2.1 below, the separate zones are listed in the project tree, and will be available for Zoning / Simulation, as rooms in their own right:
Please note that this applies to Dynamic Simulations only, ie: