Determination Of Heat Transfer In Under-Floor Plenums In Buildings With Under-Floor Air Distribution Systems

Under-Floor Air Distribution (UFAD) systems have potential advantages of energy saving and indoor air quality improvement over conventional well-mixed systems. As a ventilation strategy for buildings, a UFAD system provides conditioned air to occupied rooms through diffusers in raised floors and the air is exhausted through return grilles at the ceiling level. Many previous researches have focused on the energy saving and air quality improvement by UFAD systems because of their high supply air temperature and room air stratification. However, few of them paid attention to the effects of the heat transfer through floor slabs on the energy performance of buildings.The heat transfer across floor slabs increases the supply air temperature during the cooling mode and decreases it during the heating mode which may lead to energy loss. This thesis is to study the influence of the heat transfer through a floor slab between the under-floor plenum of a given occupied room and the downstairs return plenum on the energy performance of a typical office building. The impact of the non-uniform flow in the floor plenum was also analyzed since it affected the energy flow in the floor plenum. These factors were taken into account as well as the thermal stratification for a more rigorous and accurate energy assessment of UFAD systems. Year-round energy simulations of an office building with a UFAD system in Philadelphia were performed and compared to that with a well-mixed system