Carrier WEATHERMAKER 48/50AJ - Manual (Page 58)

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Static Pressure Set Point (SP.SP) — This is the static pres-
sure control point. It is the point against which the
ComfortLink controls compare the actual measured supply
duct pressure for determination of the error that is used for PID
control. Generally one would set SP.SP to the minimum value
necessary for proper operation of air terminals in the condi-
tioned space at all load conditions. Too high of 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 airflow.
VFD Minimum Speed (SP.MN) — This is the minimum speed
for the supply fan VFD. Typically the value is chosen to main-
tain a minimum level of ventilation.
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%.
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 ranged 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 set point. 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 set
point (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
provide 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 overpressurization. This is the recommended approach
if a third party wishes to control the variable speed supply fan.
In effect, this represents a speed control signal “pass through”
under normal operating circumstances. The ComfortLink con-
trol system overrides 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 set point 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 set point 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 venti-
lation position, to account for the drop in static pressure during
static pressure reset control. The static pressure reset for the
calculation cannot be larger than the supply air static set point
(SPSP).
The calculation is as follows:
(Static Pressure Reset/SP.LM) x (ECONOSPR –
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%.
Table 75 — Static Pressure Control Configuration
*Some defaults are model number dependent.
ITEM EXPANSION RANGE UNITS CCN POINT DEFAULT
SP SUPPLY STATIC PRESS.CFG.
SP.CF Static Pres. VFD Control? 0, 1 STATICFG 0*
SP.FN Static Pres. Fan Control? Yes/No STATPFAN Yes*
SP.S Static Pressure Sensor Enable/Disable SPSENS Disable*
SP.LO Static Press. Low Range –10 - 0 in. W.C. SP_LOW 0
SP.HI Static Press. High Range 0 - 10 in. W.C. SP_HIGH 5
SP.SP Static Pressure Setpoint 0 - 5 in. W.C. SPSP 1.5
SP.MN VFD Minimum Speed 0 - 100 % STATPMIN 20
SP.MX VFD Maximum Speed 0 - 100 % STATPMAX 100
SP.FS VFD Fire Speed Override 0 - 100 % STATPFSO 100
SP.RS Stat. Pres. Reset Config 0 - 4 SPRSTCFG 0
SP.RT SP Reset Ratio (
/dF)
0 - 2.00 SPRRATIO 0.2
SP.LM SP Reset Limit in iwc (
)
0 - 2.00 SPRLIMIT 0.75
SP.EC SP Reset Econo.Position 0 - 100 % ECONOSPR 5
S.PID STAT.PRESS.PID CONFIGS
SP.TM Static Press. PID Run Rate 1 - 200 sec SPIDRATE 2
SP.P Static Press. Prop. Gain 0 - 100 STATP_PG 20
SP.I Static Press. Intg. Gain 0 - 50 STATP_IG 2
SP.D Static Press. Derv. Gain 0 - 50 STATP_DG 0
SP.SG Static Press. System Gain 0 - 50 STATP_SG 1.0