UC San Diego

There is considerable growth in popularity of under-floor air distribution (UFAD) systems because of potential energy savings, an improvement in air quality, and thermal comfort over conventional systems. With these advantages, the UFAD system could be an alternative air distribution system potentially superior to traditional overhead system; however, well-developed design methodologies especially for under-floor plenum have not been fully explored. We have considered two issues that lower the performance of under-floor plenum in UFAD system. One is the temperature difference between diffusers results in discomfort for occupants, and the other is the heat transfer across a slab lowers energy efficiency in UFAD system. The Particle Tracking Velocimetry (PTV) experiment was conducted to demonstrate the flow pattern in the plenum, and the computational calculation by commercial FLUENT software was performed to show the flow patterns and physical properties of the flow. In this thesis, the plenum of good performance is defined as the plenum that has lower temperature variation from diffuser to diffuser and lower heat transfer rate across a slab. The objectives of this thesis are to investigate the physical properties of flow in a plenum, and give ideas for reducing temperature variation of air leaving diffusers and heat transfer across a slab.