Chilled Water Reset - T775R - Honeywell T775 Series 2000 Application Manual

T775 SERIES 2000 ELECTRONIC STAND-ALONE CONTROLLERS
Chilled Water Reset – T775R
Application Description
The T775R is controlling the chiller water temperature, based
on outside temperature using a reset curve.
Multiple stages can also be controlled by using an offset from
the main setpoint for the subsequent relay outputs. When
enabling multiple stages for reset, each stage can have its
own programmable offset from Relay 1 (stage 1).
Sensor Designation
This device application requires two sensors.
• Sensor A is sensing the water temperature of the chiller.
• Sensor B is sensing outside air temperature.
Operation
In this example, when the outside temperature reaches 90° F
(32° C), the desired water temperature of the chiller is
45° F (7° C). Likewise, when the outside temperature drops to
70° F (21° C), the chilled water temperature needs to be 60° F
(16° C).
.
°F
65
60
SP MAX A1
55
SENSOR A
(CHILLER)
50
45
SP MIN A2
40
65
RESET B1
(OUTSD MIN)
SENSOR B (OUTSIDE AIR)
Fig. 15. Chiller 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 = 1
→
— Relay 1 Reset = YES-OTHER
63-7147—05
70 90
75 80 85 95
RESET B2
(OUTSD MAX)
M24874
YES-OTHER
Relay 1: Control to the chilled water temperature
Program for: (Refer to the reset curve in Fig. 15.)
— Setpoint Max A1 (Chiller) = 60° F (16° C)
— Reset B1 (Outside Min) = 70° F (21° C)
— Setpoint Min A2 (Chiller) = 45° F (7° C)
— Reset B2 (Outside Max) = 90° F (32° C)
— Differential = 10° F (-12° C)
— 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.
IMPORTANT
By programming the Chiller setpoint at 45° F (7° C)
the T775 has established 45° F (7° C) as the lowest
operating control point that will be allowed during
reset with the above conditions satisfied.
Wiring
All output relays should have a common power wiring source,
which may or may not be the same as the T775 power wiring.
SENSOR B
(OUTSIDE AIR)
°F
CHILLER
L2
L1
(HOT)
1 POWER WITH 24 VAC OR 120/240 VAC AT THE APPROPRIATE
TERMINAL BLOCK.
2
24 VAC POWER TERMINAL BLOCK.
Fig. 16. T775R wiring — chilled water reset.
16
SENSOR A (CHILLED WATER)
T
T
T
T775R
T
2
+
C
RELAY RELAY
4 3
NC
NC
C C
NO
NO
NO
NO
C C
NC
NC
RELAY RELAY
1 2
1
120 VAC
M24875