Technical Note: Design With Vav/Constant Flow Boxes; And Ducted Applications - Price FFU-HE Series Manual

FAN FILTER UNIT - HIGH EFFICIENCY
INSTALLATION & SERVICE INSTRUCTIONS
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, caution must be taken with balancing and proper selection of fan filter unit.
A constant flow program is not recommended for this type of application. 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-HE motor shuts off. The ECM with constant torque motor program or PSC motor is suggested for this
type of application.
The FFU-HE 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. These scenarios will cause starving, or
overfeeding of the fan which can damage the fan motor. Fan filter units should be installed in a system where the inlet static will be
0.0" w.g., or slightly negative.
In ducted applications, it is critical that primary air be balanced prior to installing the FFU-HE. The primary air controls should be
locked in position post balancing, and the FFU-HE is installed and running. Similarly, the FFU-HE 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-HE is mated
with the duct. Alternatively, the Balancing Ducted Units Technical Note can also be followed on page 44 of this manual.
To prevent a high static pressure build up at the FFU-HE during start up, the FFU-HE'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.
Excessive negative static air pressure at the inlet is also not an intended use for fan filter units. Negative static at the inlet will cause
the motor to be overworked and will lead to decreased motor life. Additionally, inconsistent motor running modes may result,
depending on the magnitude of the negative pressure. Positive static inlet pressure will eventually lead to ECM motors shutting off
entirely, and PSC motors running inconsistently. The discharge static pressure of the VAV, constant flow boxes, valves, other airflow
devices, or balancing damper feeding the FFU-HE should be as close to 0.0" w.g. as possible.
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 criticalenvironments@priceindustries.com, or dial (204) 654-
5613 option 5.
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