Supply and Extract plenums are HVAC components much like Splitters and Mixers but they can be associated with a building zone which is used as the supply or extract plenum.
The only item of data required for an HVAC plenum is the name of the associated building zone.
If no zone has previously been allocated to the plenum, click on the ellipsis button adjacent to the <Select zone> text to bring up a zone selection control. Only zones that have not already been associated with zone groups or other plenums are available for selection.