Carrier XRV Specifikace stáhnout pdf (Strana 53)

6. Lead chiller temperature pulldown rate (TEMP PULL-

DOWN DEG/MIN on the TEMP_CTL screen) of the

chilled water temperature is less than 0.5 F (0.27 C) per

minute for a cumulative duration greater than the PULL-

DOWN TIMER setting in the LEAD/LAG screen.

When all the above requirements have been met, the lag

chiller is commanded to a STARTUP mode (indicated by

“CONTRL” flashing next to the CHILLER START/STOP pa-

rameter in the MAINSTAT screen). The PIC III control then

monitors the lag chiller for a successful start. If the lag chiller

fails to start, the standby chiller, if configured, is started.

Lead/Lag Pulldown Timer Operation

— Some lead/lag chill-

er applications with large chilled liquid loop volumes must ac-

commodate intermittent slugs of warm ENTERING

CHILLED WATER for short time periods. This type of tran-

sient condition can result when a control valve rapidly opens to

allow flow through a previously isolated branch or zone within

the chilled liquid system. A PULLDOWN TIMER can be con-

figured to delay starting the lag chiller so it does not excessive-

ly cycle on and off for short time periods when intermittent

slugs of warm ENTERING CHILLED WATER pass through

the chillers. A larger PULLDOWN TIMER entry gives the

warm slug of water more time to pass through the chillers be-

fore the lag chiller can start.

The chiller CONTROL POINT can be configured to either

LEAVING CHILLED WATER or ENTERING CHILLED

WATER temperature. The PIC controls monitor the tempera-

ture pulldown rate of the CHILLED WATER and display the

result as CHILL WATER PULLDOWN/MIN in the

HEAT_EX screen. Samples of the CHILLED WATER temper-

ature are taken once every 10 seconds and compared against

the previous CHILLED WATER sample. A positive value of

CHILL WATER PULLDOWN/MIN indicates that the

CHILLED WATER temperature is decreasing between succes-

sive samples. If CHILL WATER PULLDOWN/MIN rate is a

minimum of 0.5 degrees F per minute then the PULLDOWN:

SATISFIED parameter in the LL_MAINT screen displays

YES, otherwise, the PULLDOWN: SATISFIED parameter

displays NO.

If the lead chiller is unable to achieve the CONTROL

POINT, the lag chiller will not start unless the lead chiller is un-

able to maintain a CHILL WATER PULLDOWN/MIN rate of

0.5 degrees F per minute for a time period equal to the number

of minutes entered in the PULLDOWN TIMER parameter.

PULLDOWN TIME in the LL_MAINT screen displays the re-

maining delay left before the lag chiller is allowed to start

based on the pulldown timer. PULLDOWN TIME will count

down starting at the value entered in PULLDOWN TIMER

under the following conditions:

Ramp Loading is Complete

AND

PULLDOWN: SATISFIED = NO

The lag chiller pulldown start condition is met when PULL-

DOWN TIME lapses to 0.0 min.

If PULLDOWN: SATISFIED changes to YES as the

PULLDOWN TIME is counting down to zero, the PULL-

DOWN TIME will start to count back up provided that the

CHILLED WATER temperature has not fallen to less than the

CONTROL POINT plus one half of the CHILLED WATER

DEADBAND. The PULLDOWN TIME will start to count

back down again should PULLDOWN: SATISFIED change

back to NO. The PULLDOWN TIME will be immediately re-

set to the value entered in the PULLDOWN TIMER parameter

if the CHILLED WATER temperature decreases to less than

the CONTROL POINT plus one half of the CHILLED WA-

TER DEADBAND.

Lag Chiller Shutdown Requirements

— The following condi-

tions must be met in order for the lag chiller to be stopped.

1. Lead chiller AVERAGE LINE CURRENT or MOTOR

PERCENT KILOWATTS (on the MAINSTAT screen) is

less than the lead chiller percent capacity.

NOTE: Lead Chiller Percent Capacity = 115 – LAG %

CAPACITY. The LAG % CAPACITY parameter is on the

LEADLAG screen, which is accessed from the EQUIP-

MENT SERVICE table on the SERVICE menu.

2. The lead chiller chilled water temperature is less than the

CONTROL POINT temperature (see the MAINSTAT

screen) plus

the CHILLED WATER DEADBAND

temperature (see the SETUP1 screen).

3. The configured LAG STOP TIMER entry has elapsed.

The LAG STOP TIMER starts when the lead chiller

chilled water temperature is less than the chilled water

CONTROL POINT plus 1/2 of the CHILLED WATER

DEADBAND and the lead chiller compressor motor load

(MOTOR PERCENT KILOWATT or AVERAGE LINE

CURRENT on the MAINSTAT screen) is less than the

Lead Chiller Percent Capacity.

NOTE: Lead Chiller Percent Capacity = 115 – LAG %

CAPACITY. The LAG % CAPACITY parameter is on the

LEADLAG screen, which is accessed from the EQUIPMENT

SERVICE table on the SERVICE menu.

FAULTED CHILLER OPERATION — If the lead chiller

shuts down because of an alarm (*) condition, it stops commu-

nicating to the lag and standby chillers. After 30 seconds, the

lag chiller becomes the acting lead chiller and starts and stops

the standby chiller, if necessary.

If the lag chiller goes into alarm when the lead chiller is also

in alarm, the standby chiller reverts to a stand-alone CCN

mode of operation.

If the lead chiller is in an alarm (*) condition (as shown on

the ICVC panel), press the softkey to clear the alarm.

The chiller is placed in CCN mode. The lead chiller communi-

cates and monitors the RUN STATUS of the lag and standby

chillers. If both the lag and standby chillers are running, the

lead chiller does not attempt to start and does not assume the

role of lead chiller until either the lag or standby chiller shuts

down. If only one chiller is running, the lead chiller waits for a

start request from the operating chiller. When the configured

lead chiller starts, it assumes its role as lead chiller.

If the lag chiller is the only chiller running when the lead

chiller assumes its role as a lead chiller then the lag chiller will

perform a RECOVERY START REQUEST (LL_MAINT

screen). The lead chiller will start up when the following condi-

tions are met.

1. Lag chiller ramp loading must be complete.

2. Lag CHILLED WATER TEMP (MAINSTAT screen) is

greater than CONTROL POINT plus

the CHILLED

WATER DEADBAND temperature.

3. Lag chiller ACTIVE DEMAND LIMIT value must be

greater than 95% of full load amps.

4. Lag chiller temperature pulldown rate (TEMP PULL-

DOWN DEG/MIN) of the chilled water temperature is

less than 0.5 F (0.27 C) per minute.

5. The standby chiller is not running as a lag chiller.

6. The configured LAG START TIMER configured in the lag

(acting lead) chiller has elapsed. The LAG START TIMER

is started when the lag (acting lead) chiller’s ramp loading

is completed.

LOAD BALANCING — When the LOAD BALANCE OP-

TION (see LEADLAG screen) is enabled, the lead chiller sets

the ACTIVE DEMAND LIMIT in the lag chiller to the lead

chiller’s compressor motor load value MOTOR PERCENT

KILOWATTS or AVERAGE LINE CURRENT on the

RESET

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