Carrier 19XL SurgeProtection , Lead/Lag Control

The algorithm ﬁrst determines if corrective action is nec-

essary. This is done by checking 2 sets of operator con-

ﬁgured data points, which are the MINIMUM and the

MAXIMUMLoad Points, (T1/P1;T2/P2). These points have

default settings for each type of refrigerant, HCFC-22 or

HFC-134a, as deﬁned on the Service1 table, or on Table4.

These settings and the algorithm function are graphically

displayed in Fig. 20 and 21. The two sets of load points on

thisgraph (default settings are shown) describe a line which

thealgorithm uses to determine the maximum lift of the com-

pressor. Whenever the actual differentialpressure between

the cooler and condenser, and the temperature difference

betweenthe entering and leaving chilled water are above the

lineon the graph (as deﬁned by the MINIMUM and MAXI-

MUM Load Points) the algorithm will go into a corrective

action mode. If the actual values are below the line, the

algorithmtakes no action. Modiﬁcation of the default set points

ofthe MINIMUM and MAXIMUM load points is described

in the Input Service Conﬁguration section on page 50.

Correctiveaction can be taken by making one of 2 choices.

If a hot gas bypass line is present, and the hot gas is con-

ﬁgured on the Service1 table, then the hot gas bypass valve

can be energized. If a hot gas bypass if not present, then

the action taken is to hold the guide vanes. See Table4 —

Capacity Overrides. Both of these corrective actions will

reduce the lift experienced by the compressor and help to

prevent a surge condition. Surge is a condition when the

lift becomes so high that the gas ﬂow across the impeller

reverses. This condition can eventually cause chiller dam-

age.The surge prevention algorithm is intended to notify the

operator that chiller operating conditions are marginal, and

to take action to help prevent chiller damage such as low-

ering entering condenser water temperature.

SurgeProtection — Surgingof the compressor can be

determinedby the PIC through operator conﬁgured settings.

Surge will cause amperage ﬂuctuations of the compressor

motor.The PIC monitors these amperage swings, and if the

swing is greater than the conﬁgurable setting in one sec-

ond,then one surge count has occurred. The SURGE DELTA

PERCENTAMPS setting is displayed and conﬁgured on the

Service1screen. It has a default setting of 25% amps, SURGE

PROTECTIONCOUNTS can be monitored on the Maint03

table.

Asurge protection shutdown of the chiller will occur when-

ever the surge protection counter reaches 12 counts with-

in an operator speciﬁed time, known as the SURGE TIME

PERIOD. The SURGE TIME PERIOD is displayed and

conﬁgured on the Service1 screen. It has a default of

2 minutes.

Lead/Lag Control

NOTE: Lead/lag control is only available on chillers with

PSIO Software Version09 or higher.

Lead/lagis a control system process that automatically starts

and stops a lag or second chiller in a 2-chiller water system.

Referto Fig. 16 and 17 for menu, table, and screen selection

information.On chillers that have PSIO software with Lead/

Lag capability, it is possible to utilize the PIC controls to

perform the lead/lag function on 2 chillers. 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 alarm condition and additional cooling is

required.

NOTE: Lead/lag conﬁguration is viewed and edited under

Lead/Lag in the Equipment Conﬁguration table (located in

the Service menu). Lead/lag status during chiller operation

is viewed in the MAINT04 table in the Control Algorithm

Status table. See Table2.

Lead/Lag System Requirements:

• all chillers must have PSIO software capable of perform-

ing the lead/lag function

• water pumps MUST be energized from the PIC controls

• water ﬂows should be constant

• CCN Time Schedules for all chillers must be identical

LEGEND

ECW — Entering Chilled Water

HGBP — Hot Gas Bypass

LCW — Leaving Chilled Water

DP = (Condenser Psi) —(Cooler Psi)

DT = (ECW) − (LCW)

Fig. 20 — 19XL Hot Gas Bypass/Surge

Prevention

LEGEND

ECW — Entering Chilled Water

HGBP — Hot Gas Bypass

LCW — Leaving Chilled Water

DP = (Condenser kPa) — (Cooler kPa)

DT = (ECW) — (LCW)

Fig. 21 — 19XL with Default Metric Settings