Head Pressure Reference Output; Lead/Lag Control; Lead/Lag Operation; Wiring - Carrier 19XRV Start-Up, Operation And Maintenance Instructions Manual

Head Pressure Reference Output (See Fig. 24) --
The PIC [II control outputs a 4 to 20 mA signal for the
configurable Delta P (CONDENSER PRESSURE minus
EVAPORATOR PRESSURE) leference cmwe shown in Fig. 24.
The DELTA P AT 100% (chiller at maximum load condition
default at 50 psi), DELTA P AT 0% (chiller at minimum load
condition default at 25 psi) trod MINIMUM OUTPUT points
are configurable in the EQUIPMENT SERVICE-OPTIONS ta-
ble. When configuring this output ensure that minimum re-
quirements for oil pressure and proper condenser FLASC on-
lice performance are mtdntained. The 4 to 20 mA output from
VFD TBI terminals 17 and 18 may be useful as a reference
signal to control a towel bypass valve, tower speed control,
condenser pump speed control, etc. Note that it is up to the site
design engineering agent to integrate this analog output with
any external system device(s) to produce the desired effect.
Carrier does not make any claim that this output is directly us-
able to control any specific piece of equipment (that is, without
further control elements or signal conditioning), although it
may be.
The head pressure reference output will be on whenever the
condenser pump is operating. It may also be manually operated
in CONTROLS TEST. When the head pressure differential is
less than the value entered forDELTA PATO%, the output will
be maintained at 4 mA.
Lead/Lag Control
--
The lead/lag control system auto-
matically starts and stops a lag or second chiller in a 2-chiller
water system. A third chiller can be added to the lead/lag
system as a standby chiller to start up in case the lead or lag
chiller in the system has shut down during an ahum condition
and additional cooling is required. Refer to Fig. 17 and 18 for
menu, table, and screen selection information.
NOTE: The lead/lag function can be configured on the LEAD-
LAG screen, which is accessed from the SERVICE menu and
EQUIPMENT SERVICE table. See Table 4, Example 20.
Lead/lag status during chiller operation can be viewed on the
LL_MAINT display screen, which is accessed from the
SERVICE menu and CONTROL ALGORITHM STATUS
table. See Table 4, Example 12.
Lead/Lag System Requirements:
• all chillers in the system must have software capable of
performing the lead/lag function
• water pumps MUST be energized from the PIC III
controls
• water flows should be constant
• the CCN time schedules for all chillers must be identical
Operation Features:
• 2chiller lead/lag
DELTAP
AT100% "3
DE LTA P
DELTA P__
AT0%
l NON-ZERO
',EXAMPLE OF
' M N MUM
',REFERENCE
',OUTPUT
s" a"
i t
===7 = ..........
0mA 2 mA4mA
(O%)
4T0 20 mA OUTPUT
Fig. 24- Head Pressure Reference Output
]11
20 mA
(100%)
• addition of a third chiller for backup
• manual rotation of lead chiller
• load balancing if configured
• staggered restart of the chillers after a power failure
• chillers may be piped in parallel or in series chilled water
flow
COMMON POINT SENSOR USAGE AND INSTALLA-
TION- Lead/lag operation does not require a common
chilled water point sensor However. common point sensors
(Spare Temp #1 and #2) may be added to the CCM module, if
desired.
NOTE: If the common point sensor option is chosen on a
chilled water system, each chiller should have its own common
point sensor installed. Each chiller uses its own common point
sensor for control when that chiller is designated as the lead
chillel: The PIC III cannot read the value of common point
sensors installed on the other chillers in the chilled water
system.
If leaving chilled water control (ECW CONTROL OPTION
is set to 0 [DSABLEI TEMP CTL screen) and a common
point sensor is desired (COMMON SENSOR OPTION in
LEADLAG screen selected as 1) then the sensor is wired in
Spare Temp #1 position on the CCM (terminals J4-25 and
J4-J26).
If the entering chilled water control option (ECW CON-
TROL OPTION) is enabled (configured in TEMP_CTL
screen) and a common point sensor is desired (COMMON
SENSOR OPTION in LEADLAG screen selected as 1) then
the sensor is wired in Spare Temp #2 position on the CCM
(terminals J4-27 and J4-28).
When installing chillers in series, either a common point
sensor should be used (preferred), or the LEAVING CHILLED
WATER sensor of the upstremn chiller must be moved into the
leaving chilled water pipe of the downstream chillel: In this
application the COMMON SENSOR OPTION should only be
enabled for the upstremn chiller if that chiller is configured as
the Lead.
If ENTERING CHILLED WATER control is required on
chillers piped in series, either the common point return chilled
water sensor should be used (preferred), or the LEAVING
CHILLED WATER sensor of the downstream chiller must be
relocated to the LEAVING CHILLED WATER pipe of the
upstream chiller. In this application the COMMON SENSOR
OPTION should only be enabled for the downstream chiller if
that chiller is configured as the Lead. Note that ENTERING
CHILLED WATER control is not recommended for chillers
installed in series due to potential control stability problems.
To properly control the LEAVING CHILLED WATER
TEMPERATURE when chillers me piped in parallel, the water
flow through the shutdown chiller(s) should be isolated so that
no water bypass around the operating chiller occurs. However.
if water bypass around the operating chiller is unavoi&_ble, a
common point sensor in the mixed LEAVING CHILLED
WATER piping should be provided and enabled for the Lead
chillel:
CHILLER COMMUNICATION WIRING -- Refer to the
chiller's Installation Instructions, Cmrier Comfort Network
Interface section for infommtion on chiller communication
wiring.
LEAD/LAG OPERATION- The PIC III not only has the
ability to operate 2 chillers in lead/lag, but it can also start a
designated standby chiller when either the lead or lag chiller is
faulted and capacity requirements are not met. The lead/lag
option only operates when the chillel_ are in CCN mode. If any
other chiller configured for lead/lag is set to the LOCAL or
OFF modes, it will be unavailable for lead/lag operation.
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