Center for the Built Environment

Underfloor air distribution system (UFAD) is a mechanical air distribution strategy in which the conditioned air is primarily delivered to the zone from a pressurized plenum through floor-mounted diffusers. It has several potential advantages compared to conventional overhead (OH) mixing systems. However, most of the energy simulation programs widely used by the industry are not able to represent two distinct features of UFAD systems: room air stratification and the underfloor supply plenum. The situation has been improved with the development of a UFAD module in EnergyPlus. The Center for the Built Environment developed the modeling methods, tested them extensively, and conducted numerous studies of UFAD energy performance. This paper summarizes lessons learned related to UFAD specific issues such as thermal decay, sizing, terminal units, room air stratification and thermal comfort.