Maintaining Differential Temperature For Both Heating And Cooling - Honeywell T775 Series 2000 Application Manual

T775 SERIES 2000 ELECTRONIC STAND-ALONE CONTROLLERS
Maintaining Differential Temperature
for both Heating and Cooling
Application Description
This T775 program can be used to maintain a differential
temperature between Sensor A and Sensor B. This is done by
using the T775R2001, which can be used to maintain a delta
temperature between the sensors.
Sensor Description
This device application requires two sensors.
• Sensor A is sensing room temperature.
• Sensor B is sensing outside air temperature.
Operation
In this example, the T775 program energizes dampers to
open for free cooling or free heating. One relay energizes for
cooling whenever the outside temperature (Sensor B) is at
least 3ºF above the room temperature (Sensor A), and de-
energizes when the temperature drops to 1ºF above the room
temperature. A second relay energizes for heating when
temperature is at least 3ºF below the room temperature and
turns off when temp rises to 1ºF below the room temperature.
70
69
COOLING
68
OFF
67
COOLING
66
SENSOR B
ON
(OUTSIDE) °F
65
64
63
62
61
61 62 63
EXAMPLE: ROOM TEMPERATURE IS 63°F. COOLING TURNS ON
WHEN TEMP RISES TO 66°F AND TURNS OFF WHEN TEMP
FALLS TO 64°F. HEATING TURNS ON WHEN TEMP FALLS TO
60°F AND TURNS OFF WHEN TEMP RISES TO 62°F.
Fig. 40. 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:
Setting up the Sensor label names (Optional).
→ →
SETUP SENSORS SENSOR A
63-7147—05
RESET CURVE
ROOM
TEMP
HEATING
OFF
HEATING
ON
64 65 66 67 68 69 70
SENSOR A
(ROOM) °F
M32048
Select Label, then highlight ROOM A. Press  once to get
back to the SENSORS menu. Select SENSOR B. Select
Label then highlight OUTDOOR B. Choose other names if
desired.
Setting up RELAY 1 and RELAY 2 for reset.
→
SETUP OUTPUTS
→
RELAY 1 RESET = YES-OTHER (used only to set the dif-
ferential curve, do not wire Relay 1)
→
RELAY 2 RESET = YES (used for cooling)
→
RELAY 3 RESET = YES (used for heating)
Press Home to exit Setup, and press Menu to enter
programming.
RELAY 1: The below settings for RELAY 1 are to establish the
reset curve only. There will not be any electrical connec-
tions to RELAY 1. (Refer to reset curve in Fig. 40).
SP MAX A1 = 248ºF
RESET B1 = 248ºF
SP MIN A2 = -40ºF
RESET B2 = -40ºF
DIFFRENTL = N/A
HEAT/COOL = HEAT
RELAY 2: Enter the temperature delta (difference) at which
you want the cooling to turn on. In our example this value is
3ºF above the room temperature.
OFFSET= 3ºF
Next, the differential will determine the number of degrees
below the setpoint (3ºF differential) at which the cooling will
turn off. In our example this value is 2ºF
(i.e., 1°F above the room temperature).
DIFFRNTL = 2ºF
SENSOR B
(OUTDOOR
AIR TEMP.)
+
C
RELAY
4
NC
C
NO
RELAY
1 FOR 240 VAC LOAD, CONNECT TO 240 VAC TERMINAL.
Fig. 41. T775R wiring diagram for maintaining differential
temperature for both heating and cooling.
32
SENSOR A (ROOM TEMP.)
T
T
T
T
120V
COM
RELAY
3
NC
C
NO
NO NO
C C
NC NC
RELAY
1 2
1
HEAT
COOL
M32045