Resetting Zone Air Temp Based On Outside Air Temp (2 Stage Cooling) - Honeywell T775 Series 2000 Application Manual

T775 SERIES 2000 ELECTRONIC STAND-ALONE CONTROLLERS
Resetting Zone Air Temp Based on
Outside Air Temp (2 stage cooling)
Application Description
In this example, the T775L provides two stage DX cooling
based on zone temperature. The T775L calculates the zone
air temperature setpoint based on the actual outside air
temperature using a reset curve.
Sensor Description
This device application requires two sensors.
• Sensor A is sensing zone air temperature.
• Sensor B is sensing outside air temperature.
Operation
When the outdoor air temperature reaches 90 ° F the desired
zone air temp is 75 ° F, Likewise when the outside air temp
drops to 50 ° F the zone temp needs to be 68 ° F.
SP MAX A1 75
SENSOR A
ZONE AIR TEMP
70
SP MIN A2 68
65
50 55 60 65 70 75 80 85 90
RESET B1
(RETURN MIN)
Fig. 34. Zone air reset curve
63-7147—05
RESET B1
(RETURN MIN)
SENSOR B
OUTDOOR AIR TEMP M31190
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:
# RELAYS = 2
# LOOPS = 1
→
LOOP 1 # RELAYS = 2
→
LOOP 1 RESET = YES-OTHER
LOOP 1 Program for: (Refer to the reset curve in Figure 34)
- Setpoint Max A1 (Zone Max) = 75° F (24° C)
- Reset B1 (Outside Min) = 50° F (10° C)
- Setpoint Min A2 (Zone Min) = 68° F (20° C)
- Reset B2 (Outside Max) = 90° F (32° C)
- Differential = 20° F (-7° C)
- Cool.
SENSOR B
T
T
T
T
+
C
NO
C
NC
COM
NO
1 FOR 240 VAC LOAD, CONNECT TO 240 TERMINAL.
Fig. 35. T775 wiring — 2 stage cooling
28
SENSOR A
1
120V
COM
L1 (HOT)
POWER SUPPLY
NO
NO
C
LOAD 2
NC
COM
LOAD 1
M24287A
L2