Air-change effectiveness

Air-change effectiveness

The ability of an air-distribution system to provide outside air where occupants breathe. It is defined as the age of air that would occur throughout the space if the air was perfectly mixed, divided by the average age of air where occupants breathe.
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The accuracy in CRE (absolute values) is presented in Figure 9, which are comparable to the uncertainty estimated by ASHRAE Standard 129-1997 on measuring air-change effectiveness in field-based measurements of [+ or -]0.
95 as determined by the ANSI/ASHRAE Standard 129-1997, Measuring Air-Change Effectiveness, and using the 2001 ASHRAE Handbook--Fundamentals, Chapter 32, Space Air Diffusion.
In practice, two indices of ventilation effectiveness are air-change effectiveness (ACE) and pollutant removal effectiveness (PRE).