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General Electrical Controls Information
Fan Operation - Multiple Fans, With Staging
Set point and minimum variables
1. System will maintain a minimum of 3000 fpm velocity
(factory default) at the outlet of each fan, based on
the airflow monitoring station. Building Management
System (BMS) to monitor each fan nozzle actuator
feedback and keep fan speed above the minimum
required set point to maintain velocity.
2. Each fan to run at BMS defined operation for fan
staging, on or off, and event timing, as required per
system airflow requirements. BMS is also required
to control fan speed for all fans. Bypass damper
mode reference will be determined by the following
scenario listed:
A. One fan in system running, all other fans off.
Minimum flow condition.
a. One fan in operation, BMS will control fan speed
and monitor nozzle feedback as required to
maintain system set point.
b. Decreased flow condition from minimum speed.
When the speed is equal to the minimum specific
fan speed and nozzle feedback is at minimum for a
set time period (user-defined), the BMS will begin to
modulate the bypass damper(s) open to assist with
pressure control.
Increased flow condition from minimum speed. If
the bypass damper(s) are at full closed for a set
time period (user-defined), the BMS will increase
fan speed and the fan control will increase the
nozzle area as required to assist with pressure
control.
c. If one fan is at maximum speed for a set time
period, another fan may be required to keep system
set point. Note section B for multiple fan operation.
d. The PID sequence to be programmed at the BMS
for the bypass damper(s) operation. The BMS to
provide fan enable and VFD speed reference.
B. Two or more fans running, normal operation. Fan
operation normal system flow.
a. Flow requirement for system within reach of fan
operation. Fans operating will float together from
minimum speed to maximum speed to keep set
point.
b. If all fans in operation are at maximum speed for
a set time period (user-defined) and other fans are
available, another fan can be added by the BMS as
required.
c. With additional fan added to the system, all fans in
operation will decrease and match speed of new
fan until set point is reached, then fans can float
together between minimum to maximum speed.
Note section "C" if a dead band zone is created.
d. When more than one fan is operating and all are at
the minimum speed for a set time period and the
pressure is still too negative, the BMS will need to
subtract a fan.
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e. When more than one fan is in operation and any of
the fans run in the surge area for a set time period,
the BMS will need to subtract a fan or bypass
damper(s) may need to be used.
f. With the subtraction of a fan from the system, the
BMS will need to increase speed of all remaining
fans and they will float together until set point is
reached. Note section "C" if a dead band zone is
created.
g. The PID sequence to be programmed at the BMS
for the bypass damper(s) operation. The BMS to
provide fan enable and VFD speed reference.
C. Dead band in system. Flow between fans cycle
on/off.
Flow requirement for system out of reach causing
undesirable fan cycling on and off. If the fans in
the system running at full speed is not enough air
and adding an additional fan and running all fans at
minimum is too much air, then the bypass damper
mode may be necessary to settle these dead band
zones.
a. The BMS notices and counts cycling of fans to
determine dead band zone. If a dead band is
determined, the BMS will begin to modulate the
bypass damper(s) open to assist with pressure
control.
b. If the bypass damper(s) are at full closed for a set
time period, the BMS will increase fan speed and
the fan control will increase the nozzle area as
required to assist with pressure control.
c. The PID sequence to be programmed at the BMS
for the bypass damper(s) operation. The BMS to
provide fan enable and VFD speed reference.
9
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