24 Feb 99
(b) Filtered Airflow Rate. The FFA-580 is provided with an adjustable iris valve (variable
diameter orifice) at the blower inlet. The iris valve is used to maintain the airflow rate for differing
field conditions and will be field adjusted to maintain a maximum airflow rate of 311 L/s (660 cfm).
Adjusting the FFA-580 unit for this airflow rate allows the unit to maintain the minimum 283 L/s
(600 cfm) airflow rate when the HEPA filter becomes slightly loaded with dirt and atmospheric
dust. Airflow rates above 311 L/s (660 cfm) should be avoided because higher airflow rates
reduce filter adsorption capacity and residence time. The FFA-580 unit does not have a prefilter
and therefore the HEPA filter will load more quickly than a filtration system with a prefilter. The
FFA-580 unit requires periodic airflow testing to ensure it is maintaining an airflow rate in the
range of 283 L/s (600 cfm) to 311 L/s (660 cfm). An airflow rate of 283 L/s (600 cfm) will be
used for design of the overpressure filtered air system and an airflow rate of 311 L/s (660 cfm) will
be used to design the HVAC system heating and cooling loads. The FFA-580 blower unit can be
used for both 50 and 60 Hz power supply. This will result in different airflow rates and static
pressure values and needs to be considered in the facility design. The FFA-580 blower will
produce a calculated temperature rise of 4.4 degrees C (8.0 degrees F) at standard conditions.
Actual tested conditions to determine the air temperature rise across the blower unit indicated in
certain conditions the air temperature rise can be higher than the calculated value. It is
recommended that a temperature rise of 5.5 degrees C (10 degrees F) be used across the FFA-580
(2) The M49 Adsorption Filter. The M49 adsorber is a military developed and produced
gas adsorber. Quality control and testing is also provided and managed by the military. The M49
filter comes in two sizes: 283 L/s (600 cfm) and 566 L/s (1,200 cfm). The M49 adsorber is of
modular design and can be stacked in multiples to achieve a higher airflow rate. When compared
to commercially available adsorber filters, the M49 requires only one stage of filtration for an
airflow rate of 566 L/s (1,200 cfm). Therefore, using the M49 will require somewhat less floor
space than a commercial filter system. The M49 pressure drop is approximately 1,750 Pa (7 inches
wg) lower than a comparable commercially available filter. The lower static pressure drop results
in less initial blower cost due to the lower static head requirement. For CP filtration systems that
operate continuously, the lower static pressure drop of the M49 results in lower operating costs.
However, for CP systems that operate only when needed, the energy cost savings will be minor.
The M49 carbon trays are refillable by the Government. The disadvantage of the M49 filter is its
relatively high initial cost compared to commercially available filters. The M49 adsorption filter
requires prefilters, HEPA filters, and test sections or test points similar to commercial filter
systems. To procure the M49 filter, contact the Technical Director, U.S. Army Edgewood
Research, Development and Engineering Center, ATTN: SCBRD-ENP-A/ Fixed Installation
Engineer, 5183 Blackhawk Road, Aberdeen Proving Ground, MD 21010-5423.
b. Commercial Filtration Systems. Commercial filtration systems are of modular sectional
design and each section can filter 165 L/s (350 cfm) to 590 L/s (1,250 cfm) with two stages of
adsorption. The CP overpressure filter system will require, in series, the following filter sections:
roughing filter, prefilter, an initial HEPA filter, either one or two stages of adsorbers, and a final
HEPA filter. The actual type and number of filters required will depend upon what is to be