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Stratified air distribution systems such as Traditional Displacement Ventilation (TDV) and Under-Floor Air Distribution (UFAD) have been known to provide better indoor air quality. This investigation examined the influence of several key design parameters of TDV and UFAD in air distribution effectiveness.

This investigation first reviewed the literature concerning the ventilation performance of the TDV and UFAD systems. As a result, six different indoor spaces and several design parameters were selected for the parametric study. The indoor spaces were offices, classrooms, restaurants, workshops, retail shops, and auditoriums, while the design parameters were diffuser type, ventilation rate, throw, supply air temperature, and cooling load.

This investigation compared experimentally the TDV with UFAD systems that use four different diffusers (perforated TDV diffusers, swirl diffusers, linear diffusers, and perforated-floor-panel diffusers) in a test chamber that can simulate different indoor spaces of the same size. The two systems had higher ventilation performance than the mixing one under cooling mode. Also, the systems with low-height-throw diffusers were better. The experimental data was also used to validate a CFD program for studying stratified air distributions.

This investigation then used the validated CFD program to further study the ventilation performance of the TDV and UFAD systems for different indoor spaces and design parameters which were selected through the literature review. The study found that the air distribution effectiveness at breathing zone was at 1.1 ~ 1.6 for offices, classrooms, restaurants and retail shops, and at 1.6 ~ 2.0 for workshops and auditoriums. The spaces with a high ceiling such as workshops and auditoriums had higher air distribution effectiveness than those with a low ceiling. Thus, the stratified air distribution systems are better for spaces with a high ceiling. The air distribution effectiveness for the TDV and UFAD with low throw height was similar and was higher than that of UFAD with high throw height and mixing ventilation.

A database was established containing 102 cases of the parametric study results. With this database, the investigation developed a set of correlation equations for calculating air distribution effectiveness through statistical analysis. If a design case is special and the correlation equations cannot be used, this investigation proposed a seven-step guideline for using CFD to determine the air distribution effectiveness of the TDV and UFAD systems.


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