Carrier WeatherExpert 48N2 Controls, Start-Up, Operation, Service, And Troubleshooting page 83

Fan Track Initial DCFM (FT.ST)
For BP.CF = 2, this return/exhaust control configuration is the
start point upon which corrections (offset) are made over time
when FT.CF = Yes and is the constant control point for delta
cfm control when FT.CF = No.
Fan Track Max Clamp (FT.MX)
For BP.CF = 2, this return/exhaust control configuration is the
maximum positive delta cfm control value allowed.
Fan Track Max Correction (FT.AD)
For BP.CF = 2, this return/exhaust control configuration is the
max correction that is possible to be made every time a correc-
tion is made based on FT.TM. This configuration is only valid
when FT.CF = Yes.
Fan Track Internal EEPROM (FT.OF)
For BP.CF = 2, this return/exhaust control internal EEPROM
value is a learned correction that is stored in non-volatile RAM
and adds to the offset when FT.CF = Yes. This value is stored
once a day after the first correction. This configuration is only
valid when FT.CF = Yes.
Fan Track Internal RAM (FT.RM)
For BP.CF = 5, this return/exhaust control internal value is not
a configuration but a run time correction that adds to the offset
when FT.CF = Yes throughout the day. This value is only valid
when FT.CF = Yes.
Fan Track Reset Internal (FT.RS)
This option is a one-time reset of the internal RAM and inter-
nal EEPROM stored offsets. If the system is not set up right
and the offsets are incorrect, this "learned" value can be reset.
Supply Air CFM Configuration (SCF.C)
This configuration is set at the factory depending on whether a
high or low supply fan is installed. This information is then
used by the control to determine the correct cfm tables to be
used when measuring supply air cfm.
Return/Exhaust Air CFM Configuration (REF.C)
This configuration is set at the factory depending on whether a
high or low return fan is installed. This information is then
used by the control to determine the correct cfm tables to be
used when measuring return or exhaust air cfm.
Supply Air CFM Sensor (SCF.S)
This configuration allows the reading of supply air cfm when
enabled.
Return Air CFM Sensor (RCF.S)
This configuration allows the reading of return air cfm when
enabled. This sensor and ECF.S share the same analog input so
are mutually exclusive.
Exhaust Air CFM Sensor (ECF.S)
This configuration allows the reading of exhaust air cfm when
enabled. This sensor and RCF.S share the same analog input so
are mutually exclusive.
Building Pressure Run Rate (BP.TM)
For BP.CF = 1 and 2, this configuration is the PID run time rate.
Building Pressure Proportional Gain (BP.P)
For BP.CF = 1 and 2, this configuration is the PID Proportional
Gain.
Building Pressure Integral Gain (BP.I)
For BP.CF = 1 and 2, this configuration is the PID Integral
Gain.
Building Pressure Derivative Gain (BP.D)
For BP.CF = 1 and 2, this configuration is the PID Derivative
Gain.
BUILDING PRESSURE CONTROL BASED ON BP.CF
VFD Controlling Exhaust Fan Motors (BP.CF =1)
VFD controlling high capacity power exhaust consists of an
exhaust fan VFD (Outputs  FANS  E.VFD) enabled by one
power exhaust relay (Outputs  FANS  P.E.1). If building
pressure (Pressures  AIR.P  BP) rises above the building
pressure set point (BP.SP) and the supply fan is on, then build-
ing 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-minute timer will continue to re-initialize if the
VFD is still commanded to a position > 0%. If the building
pressure falls below the set point, the VFD will close automati-
cally. Any time building 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 con-
trol 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-minute timer will continue to reload 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
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 algorithm controls the return fan VFD and the
exhaust fan relay. Fan tracking is the method of control used on
the 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 air-
flow being greater of the 2) between the 2 fans. The building
pressure is controlled by maintaining this delta cfm between
the 2 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.
Whenever there is a request for the supply fan (or there is the
presence of the IGC feedback on gas heat units), the return fan
is started. The delta cfm is defined as S.CFM - R.CFM. The
return 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 ad-
justed upward or downward with a maximum adjustment at a
given instance to be no greater than Fan Track Max Correction
(FT.AD). The delta cfm cannot 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).
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