T775 SERIES 2000 ELECTRONIC STAND-ALONE CONTROLLERS
Hot Water Reset – T775R
Application Description
The T775R is controlling the boiler water temperature with two
stages (relays), based on outside temperature using a reset
curve and an offset for Relay 2.
Sensor Designation
This device application requires two sensors.
• Sensor A is sensing hot water discharge temperature of
the boiler.
• Sensor B is sensing outside air temperature
Operation
In this example, when the outside temperature reaches
70° F (21° C), the desired water temperature of the boiler is
160° F (71° C). Likewise, when the outside temperature drops
to 20° F (-7° C), the hot water temperature needs to be
210° F (99° C). See Fig. 10.
°F
220
SP MAX A1
210
(BOILER MAX)
S
200
E
N
190
S
O
180
R
A
170
160
SP MIN A2
(BOILER MIN)
150
140
10
RESET B1
(OUTSD MIN)
Fig. 10. Hot water reset curve.
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:
→
=
— MOD 1
Reset
— # Relays = 2
→
— Relay 1
Reset = YES-BOILER
→
— Relay 2
Reset = YES-BOILER
Relay 1: Control to the discharge water temperature
Program for: (Refer to the reset curve in Fig. 10.)
— Boiler Max = 210° F (99° C)
— Outside Min = 20° F (-7° C)
— Boiler Min = 160° F (71° C)
— Outside Max = 70° F (21° C)
— Differential = 20° F (-7° C)
— Sensor A
— Heat
Relay 2: Control to the discharge water temperature
Program for:
— Setpoint Offset = -10° F (-12° C) (See Fig. 11)
— Sensor A
— Heat
63-7147—05
RELAY 1
SETPOINT
RELAY 2
SETPOINT
OFFSET -10°F
20
70
30
40
50
60
80
°F
RESET B2
(OUTSD MAX)
SENSOR B
YES-BOILER
PROGRAM
RELAY 2
Fig. 11. Program mode — Relay 2 offset.
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.
IMPORTANT
By programming the boiler setpoint at 210° F (99° C)
the T775 has established 210° F (99° C) as the
highest operating point that will be allowed when the
outside temperature falls below 20° F (-7° C). As the
outside temperature increases above 20° F (-7° C),
the boiler will be reset downward per the reset ratio
until it reaches the minimum setpoint, 160° F.
Assuming an outside temperature of 20° F (-7° C), Fig. 12
describes the actions of relays 1 and 2 to control the boiler
temperature. As the boiler temperature falls below 210° F
(99° C), Relay 1 activates (Relay 1 Differential is 20° F (-7° C),
so relay closes at 190° F (88° C). If Relay 1 cannot raise the
boiler temperature and the boiler temperature continues to fall
to 180° F °, Relay 2 activates (Relay 2 differential is 20° F
(-7° C) 180° to 200° F (82° to 93° C). When the boiler is able
M24871
to reach 200° F (93° C), then Relay 2 deactivates and Relay 1
remains active until the temperature reaches 210° F (99° C).
.
DIFFERENTIAL
NOTE: The hot water reset application continues on the next
page.
14
MENU
PROGRAM
RELAY 2
OFFSET
DIFFRNTL
HEAT/COOL
SETBACK
EXIT
BOILER DISCHARGE
TEMPERATURE
210°
RELAY 1
200°
RANGE
190°
RELAY 2
DIFFERENTIAL
RANGE
180°
Fig. 12. Relay actions.
MENU
PROGRAM
RELAY 2
OFFSET
-10
o
F
ENTER
SETPOINT
OFFSET
FOR
RELAY 2
M24321
RELAY 1 OFF
RELAY 2 OFF
RELAY 1 ON
RELAY 2 ON
M24877