FIELD DETERMINATION OF PARTICLE FILTRATION EFFICIENCY

William Esposito

Ambient Group, USA

ABSTRACT

Cultural institutions in urban areas, especially in New York City, have to remove large quantities of fine particulate and gaseous compounds that are generated in the outdoor air by traffic and other air pollution sources. In order to purge agents from the air stream, these institutions expend considerable resources to design and install high-efficiency particulate filtration systems and in some cases, chemical filtration systems.

These systems displace a considerable amount of valuable floor space, their operation consumes energy and replacement materials are costly. Additionally, filter efficiencies are only certified for an individual filter, not a series of filters mounted within a fan system. As a result, facility operators have no means to verify if their filtration systems are achieving the efficiencies specified or advertised to other institutions.

The purpose of this study was to develop a field protocol to determine the true efficiency of filtration equipment while in operation in three New York City cultural institutions.

The ASTM D 2986-95a and ASHRAE 52-2P laboratory methods for filtration efficiency were adapted for field use in two separate scenarios. The first was to determine particulate sizing and concentration of ambient particles existing upstream and downstream of the filter bank utilizing an aerodynamic particle counter and sizer (fig 1). The second was to test efficiency by artificially generating small monodispersed polystyrene latex spheres (PSL) at 0.6µm and 1.2µm. These particles were generated by emulsion polymerization with an Atomizer Aerosol Generator (fig. 2).

Results revealed mean efficiencies in 3 separate HEPA equipped filter banks to be 90%, 77% and 82% for total ambient particle counts. The causes for the difference in expected and realized efficiency was investigated and it appeared, that in most cases, the decrease in efficiency could be contributed to bypass of particles around and between the installed filters in the bank and not as a result of individual filter performance. Thus, it is clear that a standardized test method should be developed and implemented to verify that installed filtration systems are achieving design intent during normal operating conditions. New particulate generation and detection technology has advanced to a level to allow verification in a field enviroment.

Fig. 1: Schematic diagram of measuring sites, upstream and downstream from filter bank.

Fig. 2: Generation of small monodispersed polystyrene latex spheres

William Esposito
Ambient Group
55 West 39th St., 12th floor
NY, NY 10018
USA
E-mail: wesposito@ambientgroup.com