Air distribution for office buildings using the plenum under a raised floor is a new concept that is beginning to be used in the United States. This concept has been in use in South Africa and Western Europe for several years, Design Considerations in applying this concept must be carefully thought out.

This paper presents the author’s approach to such a design. The mathematical manipulations of modifying a standard variable-air-volume (VAV) design into an underfloor air supply system are presented in the logic sequence developed in accomplishing the building HVAC design. Example problems and diagrams illustrate the effect of the major influencing factors.