FAN FILTER UNIT
BALANCING
Balancing: Technical Note: Design with VAV/Constant Flow Boxes and Ducted Applications
In applications where the fan filter unit will be ducted with upstream VAV, constant flow boxes, valves, or other airflow devices that
may have varying airflows, or modes, a constant flow program is not recommended.
In systems where two controllers are trying to compensate to adjust to a constant airflow, the system will be unable to stabilize.
This results in constant adjustment of both controllers until the FFU motor shuts off. The ECM with constant torque motor program
or PSC motor is suggested for this type of application.
The FFU is designed to overcome the pressure drop of the filter only. The motor is not intended to pull air down supply ductwork,
nor to experience a positive static pressure at the inlet forcing air through the fan. Fan filter units should be installed in a system
where the inlet static will be neutral or slightly negative.
In ducted applications, it is critical that primary air be balanced prior to installing the FFU. The primary air controls should be locked
in position post balancing, and the FFU is installed and running. Similarly, the FFU should be bench-set by using a flow hood and
adjusting the speed controller, as required, to the same balanced, primary airflow rate before the FFU is mated with the duct.
Alternatively, the Technical Note: Design with VAV/Constant Flow Boxes and Ducted Applications can also be followedl.
To prevent a high static pressure build up at the FFU during start up, the FFU’s should be energized prior to the system. This helps
to prevent the possibility of backwards rotations of the blower wheel, which will eventually lead to the motor shutting off.
For any additional information, or troubleshooting assistance on systems and design with fan filter units used in sequence with a
variable upstream air source, contact Price Industries Fan Filter help at [email protected], or dial
(204) 654- 5613 option 5.
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priceindustries.com | FAN FILTER UNIT - Manual
priceindustries.com | FAN FILTER UNIT - Manual
