F-F-320C
3.5.1 Metals. Metals shall be corrosion-resistant or shall be suitably processed to resist
corrosion. Dissimilar metals shall not be used in intimate contact unless they have been suitably
protected against electrolytic corrosion. Where it is necessary that any combination of such
dissimilar metals be assembled, an interposing material compatible to each shall be used. Coated
metal parts shall not be used where the electrical resistance of the surface due to the protective
finish has a deleterious effect on electrical performance. Galvanized sheet metal shall be a
commercial grade with a total zinc coating (both sides) of not less than 1.25 ounces per square
foot (381 grams per square metre).
3.6 Design. The filter units covered by this specification shall be designed for horizontal or
vertical airflow in air-conditioning and ventilating systems covered by NFPA 90A. Group 1 units
shall be of the side access design in which the collecting cells can be removed through an access
panel or door on one side of the unit. When facing the unit in the direction of the air flow, access
shall be either on the left or right side, as specified (see 6.2). Group 1 units shall be leg-mounted
or pedestal-mounted. The units shall be furnished with an integral drain pan and a drain
connection(s) of sufficient size to handle the rated volume of washwater at supply pressures to
75 pound-force per square inch gage (psig) (517 kilopascal gage (kPa (gage)). Group 2 units
shall be designed for installation in a duct system wherein access to the front and rear of the units
is provided through doors supplied and located in adjoining duct sections by the installing
contractor. The components of group 2 units shall be designed for assembly at the site without
the use of special tools. The wash systems for both group 1 and group 2 units shall operate
effectively at water supply pressures at the manifold connection as low as 30 psig (207 kPa
(gage)). The design of the filter units shall be such as to protect against or prevent conditions
which would be hazardous to personnel or deleterious to the units. When project drawings
accompany the solicitation for bids, additional design details relating to the specific installation of
the filter unit shall be as specified in the drawings.
3.7 Performance. The size of the filter units shall be designated by the rated capacity of standard
air, expressed in cfm (m3/s), which the units are designed to handle (see table I). When tested as
specified in 4.4.2, the average atmospheric dust spot efficiency at rated capacity shall be not less
than the applicable efficiency specified in table I. The mean rate of air movement through the
gross face area of the filter unit at rated capacity and efficiency shall be not less than the
applicable face velocity specified in table I. The initial resistance of the clean filter units at rated
airflow rates with after-filters in place shall be not greater than the resistance specified in table I.
The range of capacities for each group, type, style, and class shall also be as specified in table I.
3.7.1 Ozone level. The ozone concentration in the effluent air of the filter units shall be not
greater than 0.050 parts per million when tested in accordance with ARI 850.
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