Carrier XRV Especificaciones descargar pdf (Pagina 54)

MAINSTAT screen). This value has limits of 40% to 100%. In

addition, the CONTROL POINT for the lag chiller must be

modified to a value of 3 F (1.67 C) less than the lead chiller’s

CONTROL POINT value. If the LOAD BALANCE OPTION is

disabled, the ACTIVE DEMAND LIMIT and the CONTROL

POINT are both forced to the same value as the lead chiller.

AUTO. RESTART AFTER POWER FAILURE — When an

auto. restart condition occurs, each chiller may have a delay

added to the start-up sequence, depending on its lead/lag

configuration. The lead chiller does not have a delay. The

lag chiller has a 45-second delay. The standby chiller has a

90-second delay. The delay time is added after the chiller water

flow is verified. The PIC III ensures the guide vanes are closed.

After the guide vane position is confirmed, the delay for lag

and standby chillers occurs prior to energizing the oil pump.

The normal start-up sequence then continues. The auto. restart

delay sequence occurs whether the chiller is in CCN or

LOCAL mode and is intended to stagger the compressor motor

starts. Preventing the motors from starting simultaneously

helps reduce the inrush demands on the building power system.

Ice Build Control — The selectable ice build mode per-

mits use of the chiller to refreeze or control the temperature of

an ice reservoir which may, for example, be used for thermal

storage. This mode differs from water or brine chilling in that

termination (indication that the need for cooling has been

satisfied) is based on input(s) other than the temperature which

is being controlled during operation.

NOTE: For ice build control to operate properly, the PIC III

must be in CCN mode.

The PIC III can be configured for ice build operation.

• From the SERVICE menu, access the EQUIPMENT SER-

VICE table. From there, select the OPTIONS screen to

enable or disable the ICE BUILD OPTION. See Table 4,

Example 19.

•The ICE BUILD SETPOINT can be configured from the

SETPOINT display, which is accessed from the PIC III

main menu. See Table 4, Example 10.

• The ice build schedule can be viewed or modified from the

SCHEDULE table. From this table, select the ice build

schedule (OCCPC02S) screen. See Fig. 19 and the section

on Time Schedule Operation, page 25, for more information

on modifying chiller schedules.

The ice build time schedule defines the period(s) during

which ice build is active if the ice build option is enabled. If the

ice build time schedule overlaps other schedules, the ice build

time schedule takes priority. During the ice build period, the

CONTROL POINT is set to the ICE BUILD SETPOINT for

temperature control. The ICE BUILD RECYCLE and ICE

BUILD TERMINATION parameters, accessed from the

OPTIONS screen, allow the chiller operator to recycle or

terminate the ice build cycle. The ice build cycle can be

configured to terminate when:

•the ENTERING CHILLED WATER temperature is less than

the ICE BUILD SETPOINT. In this case, the operator sets

the ICE BUILD TERMINATION parameter to 0 (the default

setting) on the OPTIONS screen.

• the ICE BUILD CONTACTS input from an ice level indi-

cator are opened. In this case, the operator sets the ICE

BUILD TERMINATION parameter to 1 on the OPTIONS

screen.

• the chilled water temperature is less than the ICE BUILD

SETPOINT and the ICE BUILD CONTACTS input from

an ice level indicator are open. In this case, the operator sets

the ICE BUILD TERMINATION parameter to 2 on the

OPTIONS screen.

• the end of the ice build time schedule (OCCPC02S) has

been reached.

ICE BUILD INITIATION — The ice build time schedule

(OCCPC02S) is the means for activating the ice build option.

Ice Build is enabled if:

• a day of the week and a time period on the ice build time

schedule are enabled. The SCHEDULE screen shows an X

in the day field and ON/OFF times are designated for the

day(s),

• and the ICE BUILD OPTION is enabled.

The following events take place (unless overridden by a

higher authority CCN device).

• CHILLER START/STOP is forced to START.

•The CONTROL POINT is forced to the ICE BUILD SET-

POINT.

• Any force (Auto) is removed from the ACTIVE DEMAND

LIMIT.

NOTE: A parameter’s value can be forced, that is, the value

can be manually changed at the ICVC by an operator, changed

from another CCN device, or changed by other algorithms in

the PIC III control system.

NOTE: The Ice Build steps do not occur if the chiller is config-

ured and operating as a lag or standby chiller for lead/lag

operation and is actively being controlled by a lead chiller. The

lead chiller communicates the ICE BUILD SET POINT, the

desired CHILLER START/STOP state, and the ACTIVE

DEMAND LIMIT to the lag or standby chiller as required for

ice build, if configured to do so.

START-UP/RECYCLE OPERATION — If the chiller is not

running when ice build activates, the PIC III checks the fol-

lowing conditions, based on the ICE BUILD TERMINATION

value, to avoid starting the compressor unnecessarily:

•if ICE BUILD TERMINATION is set to the TEMP option

and the ENTERING CHILLED WATER temperature is less

than or equal to the ICE BUILD SETPOINT;

•if ICE BUILD TERMINATION is set to the CONTACTS

option and the ICE BUILD CONTACT is open;

•if the ICE BUILD TERMINATION is set to the BOTH (tem-

perature and contacts) option and the ENTERING

CHILLED WATER temperature is less than or equal to the

ICE BUILD SETPOINT and the ICE BUILD CONTACT is

open.

The ICE BUILD RECYCLE on the OPTIONS screen

determines whether or not the chiller will go into an ice build

RECYCLE mode.

• If the ICE BUILD RECYCLE is set to DSABLE (disable),

the PIC III reverts to normal (non-ice build) temperature

control when the ice build function is terminated by satisfy-

ing one of the above conditions. Once ice build is termi-

nated in this manner, it will not be reinitiated until the next

ice build schedule period begins.

• If the ICE BUILD RECYCLE is set to ENABLE, the PIC III

goes into an ICE BUILD RECYCLE mode, and the chilled

water pump relay remains energized to keep the chilled

water flowing when the compressor shuts down. If the tem-

perature of the LEAVING CHILLED WATER later increases

above the ICE BUILD SETPOINT plus half the RECYCLE

RESTART DELTA T value, the compressor restarts, control-

ling the chilled water/brine temperature to the ICE BUILD

SETPOINT.

TEMPERATURE CONTROL DURING ICE BUILD —

During ice build, the capacity control algorithm shall use the

CONTROL POINT minus 5 F (–2.8 C) for control of

the LEAVING CHILLED WATER temperature. The ECW

CONTROL OPTION and any temperature reset option shall be

ignored, if enabled, during ice build. Also, the following

control options will be ignored during ice build operation:

• ECW CONTROL OPTION and any temperature reset

options (configured on TEMP_CTL screen).

• 20 mA DEMAND LIMIT OPT (configured on

RAMP_DEM screen).

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