T775 SERIES 2000 ELECTRONIC STAND-ALONE CONTROLLERS
25 63-7147—3
4 Stage Heat and 6 Stage Cool – T775L
Application Description
The T775L is providing control for four boilers based on the
boiler's discharge water temperature and providing multistage
cooling control.
NOTE: The T775L (with up to two expansion modules) can
control any number of heating and cooling stages up
to a maximum of 12 stages.
Sensor Designation
This device application requires two sensors.
• Sensor A is sensing boiler discharge water temperature for
staged heating control.
• Sensor B is used for cooling control.
Operation
In this example, as the heating load increases, additional
stages of heat will cycle ON as the temperature decreases at
sensor A. The T775L will use four stages to provide sufficient
heating. The six cooling stages are controlled by sensor B.
NOTES:
1. The Interstage ON and OFF delay is an option for
both the heating and the cooling loops.
2. Because only 10 of the 12 relays are being used,
the remaining two relays can be used as
independent controls, each with its own setpoint
and throttling range.
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 = 10 (4 heat and 6 cool)
— # Loops = 2
— Loop 1
→ # Relays = 4
— Loop 1
→ Reset = NO
1
— Loop 2 → # Relays = 6
— Loop 2
→ Reset = NO
NOTES:
1. The Integral setup parameter can be left at the
factory default setting or adjusted as needed for
each loop.
2. The On Delay and Off Delay setup parameters
can be adjusted according to the application.
Loop 1: Control to sensor A
Program for:
— Setpoint = 200° F (93° C)
— Throttling Range = 20° F (-7° C)
— Sensor A
— Heat
— Relays = 1-4
1
Reset can be used for the T775L. However, keep in mind
that only one reset curve can be programmed. This means
that you can offset from the curve, but you cannot create a
second reset curve. Normally reset curves can be used for
Heat or Cool, not both.
Loop 2: Control to sensor B
Program for:
— Setpoint = 72° F (22° C)
— Throttling Range = 12° F (-11° C)
— Sensor B
— Cool
— Relays = 5-10
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.
Wiring
All output relays should have a common power wiring source,
which may or may not be the same as the T775 power wiring.
See Fig. 31 on page 26.
NOTE: The 4 Stage Heat and 6 Stage Cool application
continues on the next page.
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