Laboratory testing of a displacement ventilation diffuser for underfloor air distribution systems

Underfloor air distribution (UFAD) systems use the underfloorplenum beneath a raised floor to provide conditioned air through floor-mounted diffusers, which typically discharge cool air with bothhorizontal and vertical momentum components. These systems usually createa vertical temperature stratification when in cooling mode and this hasan impact on energy, indoor air quality and thermal comfort. The purposeof this study was to characterize the stratification performance of apreviously unstudied type of floor diffuser that discharges airhorizontally, with almost no vertical velocity component, and aims tocombine the benefits of both UFAD and displacement ventilation (DV)strategies.We performed 19 full scale laboratory experiments in which we varied thenumber of diffusers and the internal loads over a range of valuestypically found in office spaces. We quantified the amount of thermalstratification by measuring the dimensionless temperature at ankle heightand found a degree of stratification that is typical of DV systems -higher than is typical in UFAD systems. We developed a model based onthese results that can be used to simulate these systems in wholebuilding energy simulation tools, such as EnergyPlus, and simplified UFADdesign tools