TABLE OF CONTENTS Minimum outside air requirements should be determined according to applicable codes and standards (e.g., ASHRAE Standard 62-2001).
Some improvement in ventilation effectiveness is expected by delivering the fresh supply air near the occupant at floor or desktop level, allowing an overall floor-to-ceiling air flow pattern to more efficiently remove contaminants from the occupied zone of the space. An optimized strategy is to control supply outlets to allow mixing of supply air with room air up to the stratification height, typically no higher than head height (4 6 ft [1.2 1.8 m] depending on primary space occupancy). Above this height, stratified and more polluted air is allowed to occur. The air that the occupant breathes will have a lower percentage of pollutants compared to conventional uniformly mixed systems.
If an enhanced ventilation effectiveness ( E v) can be shown to exist in comparison to well-mixed overhead systems (see ASHRAE Standard 129 1997) the current version of Standard 62 allows some reduction in ventilation air quantities. The magnitude of this improved ventilation effectiveness will be largest during times of outside-air economizer use. The fact that the number of hours of economizer operation is typically greater for UFAD systems also contributes to overall increased ventilation effectiveness (see Chapter 11 for further discussion).
