Center for the Built Environment

The use of an underfloor plenum to deliver conditioned air directly into the occupied zone of a building is one of the key features that distinguish underfloor air distribution systems from conventional ducted overhead systems. This paper describes the development, validation, and application of a computational fluid dynamics (CFD) model for predicting the airflow and thermal performance of underfloor air supply plenums. To provide validation data for comparison with the CFD model, a series of experiments in a full-scale underfloor plenum test facility were carried out. The results of the experiments and comparison with the model predictions are described for the major variables, including plenum airflow patterns and velocities, plenum air temperature distributions, and heat exchange between the exposed concrete slab, the underside of the raised floor panels, and the supply air as it flows through the plenum. The validated CFD model was used to perform additional simulations to investigate the impact of plenum inlet design parameters (location and airflow direction and velocity) on the plenum heat gain and temperature distribution. Implications for the design and operation of underfloor air supply plenums are discussed.