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Open Access Publications from the University of California

Analysis of a hybrid UFAD and radiant hydronic slab HVAC system


In this paper, an EnergyPlus simulation model was used to simulate the operation of a novel integrated HVAC system. This system combines an underfloor air distribution system with a cooled radiant ceiling slab. A cooling tower supplies water to pre-cool the structural slabs during the night and early morning period. The paper compares the performance of this system to both an overhead system and an underfloor air distribution system in the cooling season for the Sacramento, California climate. The UFAD/Radiant hybrid system shows an energy reduction of between 21-25% during the peak cooling months, an electricity demand reduction of 27% during the peak hour, and improved occupant thermal comfort.

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