Carrier 19XL specifications Capacity Overrides

Ramp Loading Control Ð The 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-con®gured rate. The low- est temperature ramp table will be used the ®rst 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-con®gured rate.

The TEMP (Temperature) PULLDOWN, LOAD PULL DOWN, and SELECT RAMP TYPE may be viewed/modified

on the LID Equipment Con®guration table, Con®g table (see Table 2). Motor load is the default type.

Capacity Override (Table 4) Ð Capacity overrides 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 ®rst 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.

Table 4 Ð Capacity Overrides

							SECOND	OVERRIDE
			FIRST STAGE SET POINT				STAGE
OVERRIDE								TERMINATION
							SET POINT
CAPACITY
CONTROL	View/Modify
	on	Default Value			Con®gurable Range		Value	Value
	LID Screen
HIGH		HCFC-22		HFC-134a	HCFC-22	HFC-134a	.Override
	Equipment						Set Point	,Override
CONDENSER		.195 psig		125 psig	150 to 245 psig	90 to 200 psig
	Service1						+ 4 psig	Set Point
PRESSURE
		(1345 kPa)		(862 kPa)	(1034 to 1689 kPa)	(620 to 1379 kPa)	(28 kPa)
HIGH MOTOR							.Override
	Equipment	.200 F (93.3 C)			150 to 200 F (66 to 93 C)		Set Point	,Override
TEMPERATURE	Service1						+10° F	Set Point
							(6° C)
LOW
REFRIGERANT							<Trippoint	.Trippoint
TEMPERATURE	Equipment	,3° F (1.6° C)			2° to 5° F		+ Override	+ Override
(Refrigerant	Service1	(Above Trippoint)			(1° to 3° C)		DT ±1° F	DT +2° F
Override Delta							(0.56° C)	(1.2° C)
Temperature)
		HCFC-22		HFC-134a	HCFC-22	HFC-134a
		Minimum:		Minimum:
HIGH		T1 Ð 1.5° F		T1 Ð 1.5° F	0.5° to 15° F	0.5° to 15° F		Within
		(0.8° C)		(0.8° C)	(0.3° to 8.3° C)	(0.3° to 8.3° C)
								Lift Limits
COMPRESSOR	Equipment	P1 Ð 75 psid		P1 Ð 50 psid	50 to 170 psid	30 to 170 psid
								Plus Surge/
LIFT		(517 kPad)		(345 kPad)	(345 to 1172 kPad)	(207 to 1172 kPad)	None
	Service1							HGBP
(Surge		Maximum:		Maximum:
								Deadband
Prevention)		T2 Ð 10° F		T2 Ð 10° F	0.5° to 15° F	0.5° to 15° F
								Setting
		(5.6° C)		(5.6° C)	(0.3° to 8.3° C)	(0.3° to 8.3° C)
		P2 Ð 170 psid		P2 Ð 85 psid	50 to 170 psid	30 to 170 psid
		(1172 kPad)		(586 kPad)	(345 to 1172 kPad)	(207 to 1172 kPad)
MANUAL	Control							Release of
GUIDE VANE	Algorithm	Automatic			0 to 100%		None	Manual
TARGET	Maint01							Control
MOTOR LOAD Ð							>5% of	2% Lower
ACTIVE	Status01	100%			40 to 100%			Than
							Set Point
DEMAND LIMIT								Set Point

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