Carrier 30XW150-400 specifications Default 1.0 F

Table 31 — Dual Slave Chiller Control Parameters for Series Applications with Navigator Display

ITEM	ITEM EXPANSION	PATH	VALUE
MSSL	Master/Slave Select	Configuration→ RSET	Slave
			Default: Disable
			Must be set to the Slave Chiller’s address.
SLVA		Configuration→ RSET	The master and slave chiller must have
	Slave Address		different addresses and be on the same
			Bus Number
			Default: 2
LLBL		Configuration→ RSET	Range: Always Lead, Lag if Fail,
	Master Lead Lag Select		Runtime Sel
			Default: Always Lead
LLBD	Lead/Lag Balance Delta	Configuration→ RSET	Range: 40 to 400 hours
			Default: 168 hours
LLDY	Lag Start Delay	Configuration→ RSET	Range: 2 to 30 minutes
			Default: 10 minutes
LL.ER	Start If Error Higher	Configuration→ RSET	Range: 3.0 to 18 ΔF (1.7 to 10.0 ΔC)
			Default: 4.0 ΔF (2.2 ΔC)
LAG.M	Lag Unit Pump Select	Configuration→ RSET	Range: Off If U Stp, On If U Stop
			Default: Off If U Stp
LPUL	Lead Pulldown Time	Configuration→ RSET	Range: 0 to 60 minutes
			Default: 0 minutes
SERI	Chillers in Series	Configuration→ RSET	YES
			Default: NO
OPER	Operating Control Type	Operating Modes→ SLCT	CCN Control

DUAL CHILLER PUMP CONTROL FOR SERIES CHILLER APPLICATIONS — Pump control for series chill- er applications is controlled by the master chiller only. The control of the slave chiller is directed through commands emit- ted by the master chiller. The slave chiller has no action in master/slave operations. The slave chiller only verifies that CCN communication with the master chiller is present. See the Dual Chiller Sequence of Operation section on page 54.

Ramp Loading — Ramp Loading limits the rate of change of the leaving fluid temperature. If the unit is in a Cool- ing mode and configured for Ramp Loading Select (Ramp Loading Select, RL.S), the control makes two comparisons before deciding to increase capacity. First, the control calcu- lates the temperature difference between the control point and leaving fluid temperature. If the difference is greater than 4° F (2.2° C) and the rate of change (°F or °C per minute) is more than the configured Cool Ramp Loading rate (Cooling Ramp Loading, CRMP), then the control does not allow any increase of capacity.

To configure this option with the Touch Pilot display:

DISPLAY NAME	PATH	LINE NO.	VALUE
Ramp Loading	Main Menu	5	Yes
Select	→ Config→ USER
Cooling Ramp	Main Menu		Range: 0.2 to 2.0 °F
		14	(0.1 to 1.1	°C)
Loading	→ Setpoint
			Default: 1.0 °F (0.5	°C)

To configure this option with the Navigator display:

ITEM	ITEM	PATH		VALUE
	EXPANSION
RL.S	Ramp Load	Configuration→ OPTN	Yes
	Select
CRMP	Cool Ramp	Setpoints→ COOL	Range:	0.2 to 2.0 °F
				(0.1 to 1.1 °C)
	Loading		Default:	1.0 °F (0.5 °C)

Temperature Reset — Temperature reset is a value added to the basic leaving fluid temperature set point and the resulting sum of these values is the new control point. When a non-zero temperature reset is applied, the chiller controls to the new control point, not the set point. The type of temperature re- set is configured with the Cooling Reset Type (Cooling Reset Select, CRST) variable. Types of temperature reset are avail- able: Return Water Reset, Space Temperature Reset, and 4-20 mA Temperature Reset.

Under normal operation, the chiller will maintain a constant entering or leaving fluid temperature, based on the configura- tion, approximately equal to the chilled fluid set point. As the cooler load varies, the cooler fluid temperature difference will change in proportion to the load. For example, if the chiller was selected for a Entering to Leaving Water Temperature difference of 10 F (5.5 C) at full load, at 50% load the tempera- ture difference would be 5 F (2.2 C). See Fig. 19. Because the change in temperature through the cooler is a measure of the building load, the temperature difference reset is the average building load. Usually the chiller size and fluid temperature set point are selected based on a full-load condition. At part load, the fluid temperature set point may be lower than required. If the fluid temperature were allowed to increase at part load, the efficiency of the machine would increase. The chiller can also be set for return water temperature control. See Fig. 20.

Other indirect means of estimating building load and con- trolling temperature reset are also available and are discussed below.

To verify that reset is functioning correctly, subtract the Set- point Select (Current Setpoint, SETP) from the Control Point (Control Point, CTPT) to determine the degrees reset.

RETURN WATER RESET — The control system is capable of performing fluid temperature reset based on cooler fluid temperature difference. Because the change in temperature through the cooler is a measure of the building load, the tem- perature difference reset is, in effect, an average building load reset method.

Return Water Temperature Reset allows for the chilled water temperature set point to be reset upward as a function of the fluid temperature difference (building load).

NOTE: Return Water Temperature Reset should not be used with variable cooler flow rate systems.

To use Return Water Temperature Reset, four variables must be configured. Cooling Reset Type (Cooling Reset Select, CRST) must be enabled. The variable Delta T No Reset Temp (Delta T No Reset Value, CRT1) should be set to the cooler temperature difference (T) where no chilled water tem- perature reset should occur. The variable Delta T Full Reset Temp (Delta T Full Reset Value, CRT2) should be set to the cooler temperature difference where the maximum chilled water temperature reset should occur. The variable Degrees Cool Reset (Cooling Reset Deg. Value, DGRC) should be set to the maximum amount of reset desired.

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