Center for the Built Environment

This preliminary study explores the impact of various design assumptions on the supply fan energy consumption of pressurized underfloor plenum systems as compared to that of traditional overhead constant air volume (CAV) and variable air volume (VAV) systems.

The results of this study indicate that, in terms of optimizing energy efficiency, variable air volume (VAV) control of supply air is the preferred method of cooling perimeter zones of pressurized underfloor air distribution (UFAD) systems just as it is for overhead (OH) systems. Moreover, cooling fan energy consumption for underfloor VAV systems can be significantly less than that for overhead VAV systems. Results show also that constant air volume (CAV) systems can be an effective approach for zones, such as core areas, that have little load variation (assuming oversizing is minimized). For these situations a UFAD-CAV system can offer low installed cost, simplicity, and provide modest energy savings compared to an overhead VAV system.