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VFD Heating Minimum Speed (HT.V.M) — This is the low
speed setting for units in heating mode. The range is 75 to
100% with the default setting of 75%.
NOTE: Most VFDs have a built-in minimum speed adjustment
which must be configured for 0% when using ComfortLink
controls 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%
when CV.FD = Yes, the range is 33 to 67% with the default set-
ting of 67%.
VFD Fire Speed Override (SP.FS) — This is the speed that
the supply fan VFD will use during the pressurization, evacua-
tion and purge fire modes. This is usually set to 100%.
Static Pressure Reset Configuration (SP.RS) — This option
is used to configure the static pressure reset function. When
SP.RS = 0, there is no static pressure reset via an analog input.
If the outdoor air quality sensor is not configured (Configura-
tion
IAQ
IAQ.CF
OQ.A.C = 0), then it is possible to use
the outdoor air quality sensor location on the CEM board to
perform static pressure reset via an external 4 to 20 mA input.
Configuring SP.RS = 1 provides static pressure reset based
on this CEM 4 to 20 mA input and ranges from 0 to 3 in. wg.
Wire the input to the CEM using TB6-11 and 12. 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 re-
set based on SPT and defined by SP.RT and SP.LM.
Setting SP.RS to 1, 2 or 3 will give the user the ability to re-
set from 0 to 3 in. wg of static pressure. The reset will apply to
the supply static pressure setpoint. The static pressure reset
function will only act to reduce the static pressure control point.
As an example, the static pressure reset input is measuring
6 mA, and is therefore resetting 2 mA (6 mA – 4 mA) of its
16 mA control range. The 4 to 20 mA range corresponds
directly to the 0 to 3 in. wg of reset. Therefore 2 mA reset is
2/16 * 3 in. wg = 0.375 in. wg of reset. If the static pressure
setpoint (SP.SP) = 1.5 in. wg, then the static pressure control
point for the system will be reset to 1.5 – 0.375 = 1.125 in. wg.
When SP.RS = 4, the static pressure reset function acts to pro-
vide direct VFD speed control where 4 mA = 0% speed and 20
mA = 100% (SP.MN and SP.MX will override). Note that SP.CF
must be set to 1 (VFD Control), prior to configuring SP.RS = 4.
Failure to do so could result in damage to ductwork due to over-
pressurization. This is the recommended approach if a third par-
ty wishes to control the variable speed supply fan. In effect, this
represents a speed control signal "pass through" under normal
operating circumstances. The ComfortLink control system over-
rides the third party signal for critical operation situations, most
notably smoke and fire control.
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 is the static pressure
reduced for every degree below setpoint for RAT or SPT.
Static Pressure Reset Limit (SP.LM) — This option defines
the maximum amount of static pressure reset that is allowed.
This is sometimes called a "clamp."
NOTE: Resetting static pressure via RAT and SPT is primarily
a constant volume application which utilizes a VFD. The rea-
soning is that there is significant energy savings in slowing
down a supply fan as opposed to running full speed with
supply air reset. Maintaining the supply air setpoint and
slowing down the fan has the additional benefit of working
around dehumidification concerns.
Static Pressure Reset Economizer Position (SP.EC) — This
option effectively resets ECONOMIN to fully occupied ventila-
tion position, to account for the drop in static pressure during stat-
ic pressure reset control. The static pressure reset for the calcula-
tion cannot be larger than the supply air static setpoint (SPSP).
The calculation is as follows:
(Static
Pressure
Reset/SP.LM)
ECONOMIN)
As an example, the static pressure reset limit (SP.LM) =
0.75 in. wg. The current static pressure reset is set to 0.5 in. wg.
The settings for ECONOSPR = 50% and ECONOMIN = 20%.
Therefore, the amount to add to the economizer's
ECONOMIN configuration is: (0.5/0.75) x (50-20) = 20%. In
effect, for the positioning of the economizer, ECONOMIN
would now be replaced by ECONOMIN + 10%.
Static Pressure PID Config (S.PID) — Static pressure PID
configuration can be accessed under this heading in the Con-
figuration
SP submenu. Under most operating conditions the
control PID factors will not require any adjustment and the
factory defaults should be used. If persistent static pressure
fluctuations are detected, small changes to these factors may
improve performance. Decreasing the factors generally reduces
the responsiveness of the control loop, while increasing the
factors increases its responsiveness. Note the existing settings
before making changes, and seek technical assistance from
Carrier before making significant changes to these factors.
Static Pressure PID Run Rate (S.PID
number of seconds between duct static pressure readings taken
by the ComfortLink PID routine.
Static Pressure Proportional Gain (S.PID
proportional gain for the static pressure control PID control loop.
Static Pressure Integral Gain (S.PID
integral gain for the static pressure control PID control loop.
Static Pressure Derivative Gain (S.PID
derivative gain for the static pressure control PID control loop.
Static Pressure System Gain (S.PID
system gain for the static pressure control PID control loop.
STATIC PRESSURE RESET OPERATION — The Com-
fortLink controls support the use of static pressure reset. The
Linkage Master terminal monitors the primary air damper posi-
tion of all the terminals in the system (done through LINKAGE
with the new ComfortID™ air terminals).
The Linkage Master then calculates the amount of supply
static pressure reduction necessary to cause the most open
damper in the system to open more than the minimum value
(60%) but not more than the maximum value (90% or negligi-
ble static pressure drop). This is a dynamic calculation, which
occurs every two minutes whenever the system is operating.
The calculation ensures that the supply static pressure is always
enough to supply the required airflow at the worst case termi-
nal but never more than necessary, so that the primary air
dampers do not have to operate with an excessive pressure
drop (more than required to maintain the airflow setpoint of
each individual terminal in the system).
As the system operates, if the most open damper opens
more than 90%, the system recalculates the pressure reduction
variable and the value is reduced. Because the reset value is
subtracted from the controlling setpoint at the equipment, the
pressure setpoint increases and the primary-air dampers close a
little (to less than 90%). If the most open damper closes to less
than 60%, the system recalculates the pressure reduction vari-
able and the value is increased. This results in a decrease in the
controlling setpoint at the equipment, which causes the
primary-air dampers to open a little more (to greater than 60%).
The rooftop unit has the static pressure setpoint pro-
grammed into the CCN control. This is the maximum setpoint
that could ever be achieved under any condition. To simplify
the installation and commissioning process for the field, this
system control is designed so that the installer only needs to en-
ter a maximum duct design pressure or maximum equipment
pressure, whichever is less. There is no longer a need to calcu-
late the worst case pressure drop at design conditions and then
hope that some intermediate condition does not require a
55
x
(ECONOSPR
–
SP.TM) — This is the
SP.P) — This is the
SP.I) — This is the
SP.D) — This is the
SP.SG) — This is the
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