Extended-surface filters compared to conventional filters
A MERV-11 extended-surface filter bank without a pre-filter was compared to a conventional 8-pocket MERV-11 filter with a MERV-4 prefilter.
Extended surface Merv-11 filter performance was measured against conventional filters.
David Sellers, PE, senior engineer, Facility Dynamics Engineering, has reported measurements of rigid-pocket extended-surface Merv-11 filters with no prefilter. Baseline was a "fairly conventional" MERV 4 (ASHRAE Dust Spot Efficiency 20%) roll media type prefilter with a flexible 8 pocket MERV11 (ASHRAE dust spot efficiency 60-65%) bag fitler
The air handling systems are two virtually identical nominal 160,000 cfm double duct VAV units serving commercial office space in the Kaiser Permanente Building in Portland, Oregon.
His blog post has the details of the measurements and photos of the installations. Photos of the filter set up with dataloogers are provided along with plots of the performance data.