AMCA International inmotion Magazine - Fall 2011 - (Page 16)
15%) will enter the atrium through leakage paths (gaps around doors, construction cracks, and other paths) preventing positive pressurization of the atrium. The makeup air must not exceed 200 ft/min where the makeup air could come into contact with the plume unless a higher makeup air velocity is supported by an engineering analysis. Typically, such an analysis would include CFD modeling. The initial reason for this 200 ft/min limit is to prevent significant deflection of the plume and disruption of the smoke layer based on research at the National Research Council of Canada.5 This plume deflection and disruption can result in system failure, as illustrated in Figure 4. A second reason for the 200 fpm limit is to minimize the growth and spread of the fire. When makeup air is provided through open vents, the design analysis needs to minimize the potential for excessive velocity
Figure 4: Excessive makeup air velocity can cause system failure.
16
FA L L 2 0 1 1
A M C A I N T E R N AT I O N A L
inmotion
W W W. A M C A . O R G
http://WWW.AMCA.ORG
Table of Contents for the Digital Edition of AMCA International inmotion Magazine - Fall 2011