Carrier XRV Spécifications télécharger pdf (Page 52)

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 upstream chiller must be moved into the

leaving chilled water pipe of the downstream chiller. In this

application the COMMON SENSOR OPTION should only be

enabled for the upstream 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 are 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 unavoidable, a

common point sensor in the mixed LEAVING CHILLED

WATER piping should be provided and enabled for the Lead

chiller.

CHILLER COMMUNICATION WIRING — Refer to the

chiller’s Installation Instructions, Carrier Comfort Network

Interface section for information 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 chillers 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.

Lead/Lag Chiller Configuration and Operation

• A chiller is designated the lead chiller when its LEADLAG:

CONFIGURATION value on the LEADLAG screen is set

to “1.”

• A chiller is designated the lag chiller when its LEADLAG:

CONFIGURATION value is set to “2.”

• A chiller is designated as a standby chiller when its LEAD-

LAG: CONFIGURATION value is set to “3.”

• A value of “0” disables the lead/lag designation of a chiller.

This setting should also be used when “normal” operation

without regard to lead/lag rules is desired (in LOCAL or

CCN mode).

When configuring the LAG ADDRESS value on the

LEADLAG screen of chiller “A” enter the address of the

chiller on the system which will serve as lag when/if chiller

“A” is configured as lead. For example, if you are configuring

chiller A, enter the address for chiller B as the lag address. If

you are configuring chiller B, enter the address for chiller A as

the lag address. This makes it easier to rotate the lead and lag

chillers. Note that only the lag and standby chiller addresses

specified in the configured lead chiller's table are relevant at a

given time.

If the address assignments in the LAG ADDRESS

and STANDBY ADDRESS parameters conflict, the lead/lag

function is disabled and an alert (!) message displays. For

example, if the LAG ADDRESS matches the lead chiller’s

address, the lead/lag will be disabled and an alert (!) message

displayed. The lead/lag maintenance screen (LL_MAINT) dis-

plays the message ‘INVALID CONFIG’ in the LEADLAG:

CONFIGURATION and CURRENT MODE fields.

The lead chiller responds to normal start/stop controls such

as the occupancy schedule, a forced start or stop, and remote

start contact inputs. After completing start-up and ramp

loading, the PIC III evaluates the need for additional capacity.

If additional capacity is needed, the PIC III initiates the start-up

of the chiller configured at the LAG ADDRESS. If the lag

chiller is faulted (in alarm) or is in the OFF or LOCAL modes,

the chiller at the STANDBY ADDRESS (if configured) is

requested to start. After the second chiller is started and is

running, the lead chiller monitors conditions and evaluates

whether the capacity has been reduced enough for the lead

chiller to sustain the system alone. If the capacity is reduced

enough for the lead chiller to sustain the CONTROL POINT

temperatures alone, then the operating lag chiller is stopped.

If the lead chiller is stopped in CCN mode for any reason

other than an alarm (*) condition, the lag and standby chillers

are also stopped. If the configured lead chiller stops for an

alarm condition, the configured lag chiller takes the lead

chiller’s place as the lead chiller, and the standby chiller serves

as the lag chiller.

The PRESTART FAULT TIMER provides a timeout if

there is a prestart alert condition that prevents a chiller from

starting in a timely manner. If the configured lead chiller does

not complete its start-up before the PRESTART FAULT

TIMER (a user-configured value) elapses, then the lag chiller

starts, and the lead chiller shuts down. The lead chiller then

monitors the lag, acting as the lead, for a start request. The

PRESTART FAULT TIMER parameter is on the LEADLAG

screen, which is accessed from the EQUIPMENT SERVICE

table of the SERVICE menu.

If the lag chiller does not achieve start-up before the

PRESTART FAULT TIMER elapses, the lag chiller stops, and

the standby chiller is requested to start, if configured and ready.

Standby Chiller Configuration and Operation

— A chiller is

designated as a standby chiller when its LEADLAG: CONFIG-

URATION value on the LEADLAG screen is set to “3.” The

standby chiller can operate as a replacement for the lag chiller

only if one of the other two chillers is in an alarm (*) condition

(as shown on the ICVC panel). If both lead and lag chillers

are in an alarm (*) condition, the standby chiller defaults to

operate in CCN mode and will operate based on its configured

CCN occupancy schedule and remote contacts input.

Lag Chiller Start-Up Requirements

— Before the lag chiller

can be started, the following conditions must be met:

1. The lag chiller status indicates it is in CCN mode and is

not in an alarm condition. If the current lag chiller is in an

alarm condition, the standby chiller becomes the active

lag chiller, if it is configured and available.

2. Lead chiller ramp loading must be complete.

3. The configured LAG STOP TIMER entry has elapsed.

The LAG STOP TIMER starts when the lead chiller ramp

loading is completed or when a lag chiller stops. The

LAG STOP TIMER entry is on the LEADLAG screen.

4. Lead chiller ACTIVE DEMAND LIMIT (see the MAIN-

STAT screen) value must be greater than 95% of full load

amps.

5. Lead chilled water temperature must be greater than the

CONTROL POINT temperature (see the MAINSTAT

screen) plus 1/2 the CHILLED WATER DEADBAND

temperature (see the SETUP1 screen).

NOTE: The chilled water temperature sensor may be the

leaving chilled water sensor, the return water sensor, the

common supply water sensor, or the common return wa-

ter sensor, depending on which options are configured

and enabled.

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Carrier XRV Spécifications Page 52

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