INFLUENCE OF DESIGN AND OPERATING CONDITIONS ON UNDERFLOOR AIR DISTRIBUTION (UFAD) SYSTEM PERFORMANCE
Tom Webster, Tyler Hoyt, Edwin Lee, Allan Daly, Dove Feng, Fred Bauman, Stefano Schiavon, Kwang Ho Lee, Wilmer Pasut, Dan Fisher
Various methods are used to design and operate underfloor air distribution (UFAD) systems. There are a number of factors that affect UFAD performance: air distribution strategies in the supply plenum, system configuration and diffuser types, slab insulation, air handler supply temperature setpoints, operation of blinds at peak conditions, impact of occupant control, and the effect of climate differences. Generally, these factors influence performance indicators, such as plenum “thermal decay” (supply air temperature gains) and room air temperature stratification, which in turn affect system energy use and comfort conditions. Previously, the impact of design and operating strategies has been difficult to evaluate analytically due to the lack of simulation tools that accurately model the complex heat transfer processes involved with thermal decay and stratification. The development of EnergyPlus along with the recent addition of the UFAD module has progressed to the point that a systematic comparison of these strategies is now possible. In this paper, we take a detailed look at the impact of a number of design and operating variations for a medium office building prototype in Sacramento CA. A comparison to a baseline conventional VAV overhead (OH) system is included to understand better the potential energy and comfort differences between the two technologies.
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