82
(Pressures
AIR.P
BP) rises above the building pressure set
point (BP.SP) and the supply fan is on, then building pressure
control is initialized. Thereafter, if the supply fan relay goes off
or if the building pressure drops below the BP.SP minus the
building pressure set point offset (BP.SO) for 5 continuous
minutes, building pressure control will be stopped. The 5-min-
ute timer will continue to re-initialize if the VFD is still com-
manded to a position > 0%. If the building pressure falls below
the set point, the VFD will close automatically. Any time build-
ing pressure control becomes active, the exhaust fan relay turns
on which energizes the exhaust fan VFD. Control is performed
with a PID loop where:
Error = BP - BP.SP
K = 1000 * BP.TM/60 (normalize the PID control for run rate)
P = K * BP.P * (error)
I = K * BP.I * (error) + "I" calculated last time through the PID
D = K * BP.D * (error - error computed last time through the
PID)
VFD output (clamped between BP.MN and BP.MX%) = P + I
+ D
If building pressure (BP) rises above the building pressure
set point (BP.SP) and the supply fan is on, building pressure
control is initialized. Thereafter if the supply fan relay goes off
or if the building pressure drops below the BP.SP minus the
building pressure set point offset (BP.SO) for 5 continuous
minutes, building pressure control will be stopped. The 5-min-
ute timer will continue to reload if the VFD is still commanded
to a position > 0%. If the building pressure falls below the set
point, the VFD will close automatically. Any time building
pressure control becomes active, the exhaust fan relay turns on
which energizes the exhaust fan VFD.
Return/Exhaust Control (
BP.CF =2) — The fan tracking al-
gorithm controls the return fan VFD and the exhaust fan relay.
Fan tracking is the method of control used on plenum return
fan option. The ComfortLink control uses a flow station to
measure both the flow of both the supply and the return fans.
The control will measure the airflow of both the supply fan and
the return fan. The speed of the return fan is controlled by
maintaining a delta cfm (usually with supply airflow being
greater of the two) between the two fans. The building pressure
is controlled by maintaining this delta cfm between the two
fans. The higher that supply airflow quantity increases above
the return airflow, the higher the building pressure will be.
Conversely, as the return airflow quantity increases above the
supply airflow, the lower the building pressure will be. When-
ever there is a request for the supply fan (or there is the pres-
ence of the IGC feedback on gas heat units), the return fan is
started. The delta cfm is defined as S.CFM - R.CFM. The re-
turn fan VFD is controlled by a PID on the error of delta cfm
actual from delta cfm set point. If the error is positive the drive
will increase speed. If the error is negative the drive will de-
crease speed.
NOTE: These configurations are used only if Fan Tracking
Learning is enabled. When Fan Tracking Learning is enabled,
the control will adjust the delta cfm (FT.ST) between the sup-
ply and return fan if the building pressure deviates from the
Building Pressure Set Point (BP.SP). Periodically, at the rate
set by the Fan Track Learn Rate (FT.TM), the delta cfm is
adjusted upward or downward with a maximum adjustment at
a given instance to be no greater than Fan Track Max Correc-
tion (FT.AD). The delta cfm can not ever be adjusted greater
than or less than the Fan Track Initial Delta Cfm (FT.ST) than
by the Fan Track Max Clamp (FT.MX).
Smoke Control Modes — There are four smoke con-
trol modes that can be used to control smoke within areas ser-
viced by the unit: Pressurization mode, Evacuation mode,
Smoke Purge mode, and Fire Shutdown. Evacuation, Pressur-
ization and Smoke Purge modes require the controls expansion
board (CEM). The Fire Shutdown input is located on the main
base board (MBB) on terminals TB201-1 and 2. The unit may
also be equipped with a factory-installed return air smoke de-
tector that is wired to TB201-1,2 and will shut the unit down if
a smoke condition is determined. Field-monitoring wiring can
be connected to terminal TB201-1 and 2 to monitor the smoke
detector. Inputs on the CEM board can be used to put the unit
in the Pressurization, Evacuation, and Smoke Purge modes.
These switches or inputs are connected to TB202: Pressuriza-
tion — TB202-18 and 19, Evacuation — TB202-16 and 17,
and Smoke Purge — TB202-14 and 15. Refer to Major System
Components section on page 127 for wiring diagrams.
Each mode must be energized individually on discrete in-
puts and the corresponding alarm is initiated when a mode is
activated. The fire system provides a normally closed dry
contact closure. Multiple smoke control inputs, sensed by the
control will force the unit into a Fire Shutdown mode.
FIRE SMOKE INPUTS — These discrete inputs can be
found on the local display under Inputs
FIRE.
Fire Shutdown Mode
— This mode will cause an immediate
and complete shutdown of the unit.
Pressurization Mode
— This mode attempts to raise the pres-
sure of a space to prevent smoke infiltration from an adjacent
space. Opening the economizer (thereby closing the return air
damper), shutting down power exhaust and turning the indoor
fan on will increase pressure in the space.
Evacuation Mode
— This mode attempts to lower the pres-
sure of the space to prevent infiltrating an adjacent space with
its smoke. Closing the economizer (thereby opening the return-
air damper), turning on the power exhaust and shutting down
the indoor fan decrease pressure in the space.
Smoke Purge Mode
— This mode attempts to draw out
smoke from the space after the emergency condition. Opening
the economizer (thereby closing the return-air damper), turning
on both the power exhaust and indoor fan will evacuate smoke
and bring in fresh air.
AIRFLOW CONTROL DURING THE FIRE/SMOKE
MODES — All non-smoke related control outputs will get
shut down in the fire/smoke modes. Those related to airflow
will be controlled as explained below. The following matrix
specifies all actions the control shall undertake when each
mode occurs (outputs are forced internally with CCN priority
number 1 - “Fire”):
*“FSO” refers to the supply and exhaust VFD fire speed override
configurable speed.
SMOKE CONTROL CONFIGURATION
The economizer’s commanded output can be found in
Outputs
ECON
ECN.C.
The configurable fire speed override for supply fan VFD is in
Configuration
SP
SP.FS.
The supply fan relay’s commanded output can be found in
Outputs
FANS
S.FAN.
The supply fan VFD’s commanded speed can be found in
Outputs
FANS
S.VFD.
ITEM EXPANSION RANGE
CCN
POINT
WRITE
STATUS
FIRE FIRE-SMOKE INPUTS
FSD Fire Shutdown Input ALRM/NORM FSD forcible
PRES Pressurization Input ALRM/NORM PRES forcible
EVAC Evacuation Input ALRM/NORM EVAC forcible
PURG Smoke Purge Input ALRM/NORM PURG forcible
DEVICE PRESSURIZATION PURGE EVACUATION FIRE SD
Economizer 100% 100% 0% 0%
Indoor Fan —
VFD
ON/FSO* ON/FSO* OFF OFF
Power Exhaust
VFD
OFF ON/FSO* ON/FSO* OFF
Heat Interlock
Relay
ON ON OFF OFF
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