Honeywell T775B Series User Manual

T775 SERIES 2000 ELECTRONIC STAND-ALONE CONTROLLERS
29 63-7147—05
Resetting Discharge Air Temp Based
on Return Air Temp
(Modulating cooling valve)
Application Description
The T775R is controlling discharge air temperature based on
return air temp using a reset curve.
The T775R calculates the discharge temp setpoint based on
the actual return temp in the air handling unit.
Sensor Description
This device application requires two sensors:
• Sensor A is sensing discharge air temperature.
• Sensor B is sensing return air temperature.
Operation
In this example, the T775R controls an actuator, based on the
discharge temperature setpoint to modulate the cool water
valve.
When the return air temperature reaches 75, the desired
discharge air temp is 50. Likewise when the return air temp
drops to 70, the discharge temp needs to be 60.
Fig. 36. Discharge air 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 = YES-OTHER
MOD1 Program for: (Refer to the reset curve in Figure 36)
- Setpoint Max A1 (Discharge Max) = 60° F (16° C)
- Reset B1 (Return Min) = 70° F (21° C)
- Setpoint Min A2 (Discharge Min) = 50° F (10° C)
- Reset B2 (Return Max) = 75° F (24° C)
- Throttling Range = 10° F (-12° C)
- Cool.
Fig. 37. T775 wiring — valve modulation
65
50SP MIN A2
SP MIN A1
55
SENSOR A
DISCHARGE AIR
TEMP
RESET B1
(RETURN MIN)
RESET B2
(RETURN MAX)
60
70 75 80
M31191
SENSOR B RETURN AIR TEMP
M31192
ML7425
SPRING RETURN
VALVE
ACTUATOR
WIRING
STRIP
F
+
T2
T1
O1
O2
TS
–
L1
HOT)
L2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.
1
24 VAC POWER TERMINAL BLOCK.
2
1
SENSOR A
(DISCHARGE AIR TEMP
SENSOR B
(RETURN AIR TEMP)
T
T
C
S
V
B
R
W
+
–
MOD 1
T775R
C
+
2

Honeywell T775B Series Specifications

General

Brand	Honeywell
Model	T775B Series
Category	Controller
Language	English