2.2.9 Plenums

Plenums are spaces above the ceiling and below the floor above where lighting fixtures, pipes, ducts and other building services are often located. Plenums may or may not be used as return air plenums. Because of the leakage through the ceiling (typically suspended with lay-in panels), the temperature of the plenum tracks the temperature of the space, except that it is generally warmer because of heat stratification and heat produced by lighting fixtures located at the ceiling or in the plenum.

It is generally recommended that plenums be modeled as separate thermal blocks, but at the modeler’s discretion, they may be combined with conditioned space below for modeling simplicity.