Carrier WeatherExpert 48N2 Controls, Start-Up, Operation, Service, And Troubleshooting page 70

Static Pressure Configuration (SP.CF)
This variable is used to configure the use of ComfortLink for
static pressure control. It has the following options:
• 0 (DISABLED) - No static pressure control by Com-
fortLink controls. This would be used for a constant vol-
ume (CV) application when static pressure control is not
required or for a VAV application if there will be third-par-
ty control of the VFD. In this latter case, a suitable means
of control must be field-installed.
• 1 (ENABLED) - This will enable the use of ComfortLink
controls
Staged Air Volume Control (SP.SV)
This variable enabled the use of a CV unit with VFD for staged
air volume control.
Static Pressure Sensor (SP.S)
This variable enables the use of a supply duct static pressure
sensor. This must be enabled to use ComfortLink controls for
static pressure control. If using a third-party control for the
VFD, then this should be disabled.
Static Pressure Low Range (SP.LO)
This is the minimum static pressure that the sensor will mea-
sure. For most sensors this will be 0 in. wg. ComfortLink con-
trols will map this value to a 4 mA sensor output.
Static Pressure High Range (SP.HI)
This is the maximum static pressure that the sensor will mea-
sure. Commonly this will be 5 in. wg. The ComfortLink con-
trols will map this value to a 20 mA sensor output when the
signal is 20 mA.
Static Pressure Set Point (SP.SP)
This is the static pressure control point. It is the point against
which ComfortLink controls compares the actual measured
supply duct pressure for determination of the error that is used
for PID control. Adjust SP.SP to the minimum value necessary
for proper operation of air terminals in the conditioned space at
full load and part load. Too high a value will cause unnecessary
fan motor power consumption at part load conditions and/or
noise problems. Too low a value will result in insufficient air-
flow.
VFD Minimum Speed (SP.MN)
This is the minimum speed for the supply fan VFD. Typically
the value is chosen to maintain a minimum level of ventilation.
NOTE: Most VFDs have a built-in minimum speed adjustment
that should be configured for 0% when using ComfortLink con-
trols for static pressure control.
VFD Maximum Speed (SP.MX)
This is the maximum speed for the supply fan VFD. This is
usually set to 100%.
VFD Fire Speed Override (SP.FS)
This is the speed that the supply fan VFD will use during the
fire modes: pressurization, evacuation, and purge. This is usu-
ally set to 100%.
ITEM
Inputs
 4-20  SP.M Static Pressure mA
 4-20  SP.M.T Static Pressure mA Trim
 RSET  SP.RS Static Pressure Reset
 4-20  SP.M Static Pressure Reset mA
Outputs
 FANS  S.VFD Supply Fan VFD Speed
Table 47 — Static Pressure Reset Related Points
EXPANSION
4 to 20
–2.0  +2.0
0.0 to 3.0
4 to 20
0 to 100
Static Pressure Reset Configuration (SP.RS)
This option is used to configure the static pressure reset func-
tion. When SP.RS = 0, there is no static pressure reset via an
analog input. When SP.RS = 1, there is static pressure reset
based on the CEM 4 to 20 mA input and ranged from 0 to 3 in.
wg. When SP.RS = 2, there is static pressure reset based on
RAT and defined by SP.RT and SP.LM. When SP.RS = 3, there
is static pressure reset based on SPT and defined by SP.RT and
SP.LM. When SP.RS = 4, there is VFD speed control where
4 mA = 0% speed and 20 mA = 100% (SP.MN and SP.MX will
override).
Static Pressure Reset Ratio (SP.RT)
This option defines the reset ratio in terms of static pressure
versus temperature. The reset ratio determines how much the
static pressure is reduced for every degree below set point for
RAT or SPT.
Static Pressure Reset Limit (SP.LM)
This option defines the maximum amount of static pressure re-
set that is allowed. This is sometimes called a "clamp."
NOTE: Resetting static pressure via RAT and SPT is primarily
a constant volume application that utilizes a VFD. The reason-
ing is that there are significant energy savings in slowing down
a supply fan as opposed to running full speed with supply air
reset. Maintaining the supply air set point and slowing down
the fan has the additional benefit of working around dehumidi-
fication concerns.
Static Pressure PID Config (S.PID)
Static pressure PID configuration can be accessed under this
heading in the Configuration  SP submenu. Under most oper-
ating conditions, the control PID factors will not require any
adjustment and the factory defaults should be used. If per-
sistent static pressure fluctuations are detected, small changes
to these factors may improve performance. Decreasing the fac-
tors generally reduce the responsiveness of the control loop,
while increasing the factors increase its responsiveness. Note
the existing settings before making changes, and seek technical
assistance from Carrier service personnel before making sig-
nificant changes to these factors.
Static Pressure PID Run Rate (S.PID  SP.TM) — This is the
number of seconds between duct static pressure readings taken
by the ComfortLink PID routine.
Static Pressure Proportional Gain (S.PID  SP.P) — This is
the proportional gain for the static pressure control PID control
loop.
Static Pressure Integral Gain (S.PID  SP.I) — This is the in-
tegral gain for the static pressure control PID control loop.
Static Pressure Derivative Gain (S.PID  SP.D) — This is the
derivative gain for the static pressure control PID control loop.
RELATED POINTS
These points represent static pressure control and static pres-
sure reset inputs and outputs. See Table 47.
RANGE UNITS
mA
mA
in. wg
mA
%
70
CCN POINT DEFAULT
SP_MA
SPMATRIM
SPRESET 0.0
SP_MA 0.0
SFAN_VFD