T775 SERIES 2000 ELECTRONIC STAND-ALONE CONTROLLERS
63-7147—05 20
Multi-Stage Chiller Control (No
Reset) – T775P
Application Description
The T775P is providing multistage cooling control based on
the chiller’s discharge water temperature. The T775P uses
the fourth output relay to energize the primary pump.
Any number of stages from 1 to 12 can be configured (T775P
and T775L models). The throttling range is divided equally
among the stages.
Sensor Designation
This device application requires three sensors.
• Sensor A is sensing chiller discharge water and is used to
control 3 chiller stages.
• Sensor B is sensing outside temperature and is used to
control Relay 4, the pump output.
• Sensor C is sensing the chiller return water temperature.
NOTE: Control can be to either Sensor A or C.
Operation
In this 3-stage example, as the cooling load increases,
additional stages of cooling will cycle ON as the chiller water
temperature increases. The T775P will stage three chillers to
provide sufficient cooling. See Fig. 23 for staging behavior.
The primary circulating pump energizes whenever any stage
is energized.
Programming Example
Program in Setup:
Press and hold the MENU button for 5 seconds to enter
Setup mode. Select the Outputs menu, and then select:
— # Stages = 3 (T775 assigns pump to Relay 4)
— Options
→ On Delay and Off Delay:
Seconds = 0 to 3,600 (default is 0)
— STG4/Pump: (Relay 4 controls the pump output)
1
Enable = YES
Exercise = YES or NO
Prepurge = -300 to 300 seconds (default is 0)
Postpurge = 0 to 300 seconds (default is 0)
Return to the Setup menu, and select Alarms:
— Low Alarm = YES
— Low Limit = 54° F (12° C)
Stages 1-3: Control to the discharge water temperature
Program for:
— Setpoint = 72° F (22° C)
— Throttling Range = 12° F (-11° C)
— Sensor A
—Cool
IMPORTANT
After the desired value is selected, be sure to press
the or or HOME button in order to save that
value in the controller’s memory.
1
See Notes in See “Programming Example” on page 17. for
an explanation of Prepurge and Postpurge times.
Fig. 23. Chiller control staging behavior (when the
effective setpoint = 72° F).
Wiring
All output relays should have a common power wiring source,
which may or may not be the same as the T775 power wiring.
See Fig. 24.
Fig. 24. T775P wiring — multi-stage chiller control
(no reset).
M28009
STAGE 2 ON
STAGE 3 ON
STAGE 1 ON
-33%
STAGES
HYST.
0% 33% 67%
STAGE 1
STAGE 2
STAGE 3
1
1
CHILLER DISCHARGE WATER TEMPERATURE
68°F 72°F 76°F 80°F
STAGE ENERGIZES STAGE DE-ENERGIZES
THROTTLING RANGE (12°F)
T
T
M28008
T
T
SENSOR A
(CHILLER DISCHARGE WATER)
C
NO
NC
C
NO
NC
C
NC
NO
C
NC
NO
T
T
RELAY
1
C
+
RELAY
4
RELAY
3
RELAY
2
T775P
SENSOR C
(CHILLER
RETURN WATER)
SENSOR B (OUTSIDE AIR)
120
COM
240
1
2
120 VAC
L1
(HOT)
L2
CHILLER 1
L1
(HOT)
L2
CHILLER 2
CHILLER 3
PUMP
POWER WITH 24 VAC OR 120/240 VAC AT THE APPROPRIATE TERMINAL BLOCK.
24 VAC POWER TERMINAL BLOCK.
1
2
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