Ramp Loading Control; Capacity Override - Carrier 19XL Start-Up, Operation And Maintenance Instructions Manual

Ramp Loading Control —
slows down the rate at which the compressor loads up. This
control can prevent the compressor from loading up during
the short period of time when the chiller is started, and the
chilled water loop has to be brought down to normal design
conditions. This helps reduce electrical demand charges by
slowly bringing the chilled water to control point. However,
the total power draw during this period remains almost
unchanged.
There are 2 methods of ramp loading with the PIC. Ramp
loading can be based on chilled water temperature or on mo-
tor load.
1. Temperature ramp loading limits the rate at which either
leaving chilled water or entering chilled water temper-
ature decreases by an operator-configured rate. The low-
est temperature ramp table will be used the first time the
chiller is started (at commissioning). The lowest tem-
perature ramp rate will also be used if chiller power has
been off for 3 hours or more (even if the motor ramp load
is selected).
2. Motor load ramp loading limits the rate at which the
compressor motor current or compressor motor load
increases by an operator-configured rate.
The TEMP (Temperature) PULLDOWN, LOAD PULL
DOWN, and SELECT RAMP TYPE may be viewed/modified
OVERRIDE
CAPACITY
View/Modify
CONTROL
on
LID Screen
HIGH
Equipment
CONDENSER
Service1
PRESSURE
HIGH MOTOR Equipment
TEMPERATURE Service1
LOW
REFRIGERANT
TEMPERATURE Equipment
(Refrigerant Service1
Override Delta
Temperature)
HIGH
COMPRESSOR
Equipment
LIFT
Service1
(Surge
Prevention)
MANUAL Control
GUIDE VANE Algorithm
TARGET Maint01
MOTOR LOAD —
ACTIVE Status01
DEMAND LIMIT
The ramp loading control
Table 4 — Capacity Overrides
FIRST STAGE SET POINT
Default Value
HCFC-22 HFC-134a
195 psig 125 psig
(1345 kPa) (862 kPa)
200 F (93.3 C)
3° F (1.6° C)
(Above Trippoint)
HCFC-22 HFC-134a
Minimum: Minimum:
T1 — 1.5° F T1 — 1.5° F
(0.8° C) (0.8° C)
P1 — 75 psid P1 — 50 psid
(517 kPad) (345 kPad)
Maximum: Maximum:
T2 — 10° F T2 — 10° F
(5.6° C) (5.6° C)
P2 — 170 psid P2 — 85 psid
(1172 kPad) (586 kPad)
Automatic
100%
on the LID Equipment Configuration table, Config table (see
Table 2). Motor load is the default type.
Capacity Override (Table 4) —
can prevent some safety shutdowns caused by exceeding
motor amperage limit, refrigerant low temperature safety limit,
motor high temperature safety limit, and condenser high pres-
sure limit. In all cases there are 2 stages of compressor vane
control.
1. The vanes are held from opening further, and the status
line on the LID indicates the reason for the override.
2. The vanes are closed until condition decreases below the
first step set point, and then the vanes are released to nor-
mal capacity control.
Whenever the motor current demand limit set point is reached,
it activates a capacity override, again with a 2-step process.
Exceeding 110% of the rated load amps for more than
30 seconds will initiate a safety shutdown.
The compressor high lift (surge prevention) set point will
cause a capacity override as well. When the surge preven-
tion set point is reached, the controller normally will only
hold the guide vanes from opening. If so equipped, the hot
gas bypass valve will open instead of holding the vanes.
Configurable Range
HCFC-22 HFC-134a
150 to 245 psig 90 to 200 psig
(1034 to 1689 kPa) (620 to 1379 kPa)
150 to 200 F (66 to 93 C)
2° to 5° F
(1° to 3° C)
HCFC-22 HFC-134a
0.5° to 15° F 0.5° to 15° F
(0.3° to 8.3° C) (0.3° to 8.3° C)
50 to 170 psid 30 to 170 psid
(345 to 1172 kPad) (207 to 1172 kPad)
0.5° to 15° F 0.5° to 15° F
(0.3° to 8.3° C) (0.3° to 8.3° C)
50 to 170 psid 30 to 170 psid
(345 to 1172 kPad) (207 to 1172 kPad)
0 to 100%
40 to 100%
31
Capacity overrides
SECOND
OVERRIDE
STAGE
TERMINATION
SET POINT
Value Value
Override
Set Point Override
+ 4 psig Set Point
(28 kPa)
Override
Set Point Override
+10° F Set Point
(6° C)
Trippoint Trippoint
+ Override + Override
T –1° F T +2° F
(0.56° C) (1.2° C)
Within
Lift Limits
Plus Surge/
None
HGBP
Deadband
Setting
Release of
None Manual
Control
2% Lower
5% of
Than
Set Point
Set Point