Multi-Stage Boiler Control (Reset) - T775P - Honeywell T775 Series 2000 Application Manual

T775 SERIES 2000 ELECTRONIC STAND-ALONE CONTROLLERS
Refer to the staging diagram in Fig. 18 for individual stage
behavior.
STAGE 3 ON
STAGE 2 ON
STAGE 1 ON
STAGE 1
-33%
1 206°F
THROTTLING RANGE (18°F)
STAGE ENERGIZES
DISCHARGE WATER TEMPERATURE
1
Fig. 18. Boiler control staging behavior (when the
effective setpoint = 200° 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. 19.
SENSOR C
(RETURN WATER)
NO
DIGITAL OUTPUT
C
ALARM
NC
NC
C
NO
2
+
C
RELAY
4
L1
NC
(HOT)
PUMP
L2
NO
BOILER #1
L1
(HOT)
L2 BOILER #2
BOILER #3
1 POWER WITH 24 VAC OR 120/240 VAC AT THE APPROPRIATE
TERMINAL BLOCK.
2
24 VAC POWER TERMINAL BLOCK.
Fig. 19. T775P wiring — multi-stage boiler control
(no reset).
63-7147—05
STAGES
HYST.
STAGE 3
STAGE 2
0% 33% 67%
200°F 194°F 188°F
STAGE DE-ENERGIZES
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SENSOR A (DISCHARGE WATER)
T
T
T775P
T
T
RELAY
3
NC
C
C
NO
NO NO
C
C
NC NC
RELAY RELAY
1 2
Multi-Stage Boiler Control (Reset) –
T775P
Application Description
The T775P is providing multistage boiler control based on the
boiler'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 discharge water and is used to control
3 boiler stages.
• Sensor B is sensing outside temperature and is used for
reset.
• Sensor C is sensing the return water temperature.
NOTE: Control can be to either Sensor A or C.
Operation
In this 3-stage example, as the heating load increases,
additional stages of heat will cycle ON as the boiler water
temperature decreases. The T775P will stage three boilers to
provide sufficient heating. See Fig. 20 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
— Options
Seconds = 0 to 3,600 (default is 0)
— Options
Temperature = 30 to 100° F (-1 to 38° C)
— STG4/Pump: (Relay 4 controls the pump output)
Enable = YES
Exercise = YES or NO
Prepurge = -300 to 300 seconds (default is 0)
Postpurge = 0 to 300 seconds (default is 0)
1
Return to the Setup menu, and select Alarms:
120 VAC
— High Alarm = YES
— High Limit = 220° F (104° C)
Stages 1-3: Control to the discharge water temperature
Program for: (Refer to the reset curve in Fig. 21.)
— Boiler Max = 210° F (99° C)
— Outside Min = 20° F (-7° C)
— Boiler Min = 160° F (71° C)
— Outside Max = 70° F (21° C)
— Throttling Range = 18° F (-8° C)
— Sensor A
— Heat
— Setback = -10° F (-12° C) (Optional)
1
See Notes in "Programming Example" on page 18 for an
M24866
explanation of Prepurge and Postpurge times.
18
→
Reset = YES-BOILER
→
On Delay and Off Delay:
→
WWSD = YES or NO
1