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Open Access Publications from the University of California

A comparison between two underfloor air distribution (UFAD) design tools


The purpose of this study is to compare the capabilities and accuracy of two publicly available underfloor air distribution (UFAD) design tools (ASHRAE RP-1522 and CBE). The comparison is based on the air distribution models, diffuser types, ability to predict the design cooling load, supply plenum heat balance, temperature profile and setpoint, plenum configuration, and air distribution effectiveness. A combined database is fed into each tool’s air distribution model to assess their accuracy. The results show the RP-1522 model predicts thermal stratification slightly more accurately than the CBE model in cases using swirl and square diffusers, but both results are comparably accurate for design purposes. The CBE UFAD tool has the key advantage of being able to predict the UFAD cooling load and model four different plenum configurations and both interior and perimeter zones. The RP-1522 tool is able to calculate the air distribution effectiveness.

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