Using The T775R As A Differential Temperature Controller For Solar Water Heating - Honeywell T775 Series 2000 Application Manual

T775 SERIES 2000 ELECTRONIC STAND-ALONE CONTROLLERS
Using the T775R as a Differential
Temperature Controller for Solar
Water Heating
Application Description
The T775 can be used as a differential temperature controller
for solar water heating applications. The controller regulates
the circulation of water between the solar energy collector and
the water storage tank. The circulation pump turns on/off
based on the desired (predetermined) temperature differential
between the collector and the tank.
Sensor Description
This device application requires two sensors:
• Sensor A is sensing collector water temperature.
• Sensor B is sensing storage water temperature.
Operation
Programming example: Settings may be changed according
to geographical location, equipment, and other preferences.
Pump turns on when there is a 25°F differential between the
solar collector water temperature and the storage tank
temperature and turns off when the differential is 5°F.
High limit shut off or alarm at 190°F.
Optional low temperature purge or alarm at 40°F.
240
220
180
PUMP TURNS ON
160
140
COLLECTOR
120
WATER
100
TEMPERATURE
(°F) 80
60
40
20
0
0 20 40 60
STORAGE WATER TEMPERATURE (°F)
Fig. 38. Reset curve.
63-7147—05
RESET CURVE
STORAGE TANK
TEMPERATURE
PUMP TURNS OFF
EX: STORAGE TANK TEMPERATURE OF
80°F, PUMP TURNS ON AT 105°F AND
OFF AT 85°F
80 100 120 140 160 180 200 220
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
Select Label then highlight DISCHRG A. Press the  once to
get back to the SENSORS menu. Select SENSOR B.
Select Label then highlight RETURN 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
→
RELAY 3 RESET = YES
Press Home to exit Setup, and press Menu to enter
programming.
RELAY 1: The below settings for RELAY 1 are to establish the
offset curve only. There will not be any electrical connec-
tions to RELAY 1. (Refer to reset curve in Fig. 38).
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 differential at which you want
the pump to turn on. In our example this value is 25°F.
- OFFSET = 25°F
Next you must determine the value at which you want the
pump to shut off. The differential will determine the number of
degrees below the setpoint (25°F differential) at which the
pump will turn off. In our example this value is 20°F (i.e., 5°F
above the storage tank temperature).
- DIFFRNTL = 20°F
- HEAT
RELAY 3: Enter the high limit temperature. The pump will shut
240
off if the return water temperature from the storage tank
reaches this temperature. In our example this value is
M32047
190°F.
- SETPOINT = 190°F
- DIFFRTL = 5°F
- SENSOR: SENSOR B
- HEAT
RELAY 4: Enter the low limit temperature. An alarm will turn
on or valve will close when the return water from the stor-
age tank reaches this temperature. In our example this
value is 40F.
- SETPOINT = 40°F
- DIFFRTL = 2°F
- SENSOR: SENSOR B
- HEAT
30
→
SENSOR A