T8501 AND T8511 DELUXE ELECTRONIC THERMOSTATS
68-0162—1
11
OPERATION
Thermal Performance
During severe weather, the thermostat actually controls closer
to the setpoint than a conventional control. This is because
the heat anticipator is replaced by two electronic control
strategies—cycling by heat anticipation and proportional plus
integral control.
Electronic cycling by heat anticipation acts like a traditional
heat anticipator except that it never needs adjusting for
various control circuit load currents. It cycles the heating
system off slightly before the room temperature reaches the
setpoint to keep the heat left in the ductwork from overheating
the room.
In severe weather, a conventional control with a heat
anticipator tends to turn off the system too soon so the
effective setpoint is somewhat below the setpoint. In very cold
weather, the difference between setpoint and effective control
point can be 5°F or 6°F (2°C or 3°C) with a conventional
control. This phenomenon is called
droop
.
Proportional plus integral action eliminates droop by adjusting
the on time of the stage that is cycling longer or shorter until
the control point matches the setpoint. The thermostat
maintains the space temperature within 1°F of the setpoint.
The
zero droop
performance provides improved occupant
comfort and energy savings. Occupants do not need to
continually adjust thermostat settings to maintain desired
temperature, even during severe weather.
Operation Sequence
The thermostat energizes specific terminals depending what
the Fan and System are set to. The LCD will display symbols
and words to report the condition of system. See Tables 7 and
8 for specific information.
Table 7. T8501 Sequence of Operation.
Fan
Selection
System
Selection Call Energize Display
a
Auto Off None None None
On Off None G
Auto Cool None
O
b
None
Auto Cool or Auto Cooling
O
b
, G, Y
and
Auto Heat None
B
b
None
Auto Heat or Auto Heating
B
b
, W
c
Auto Auto None
O or B
d
None
a
System selection is displayed.
b
Only available on select models.
c
When electric heat fan is selected, G is energized and fan
symbol is displayed.
d
Based on last piece of equipment called (cooling = O or
heating = B) and Installer Setup selection.
Table 8. T8511 Sequence of Operation for Separate Compressor Terminal (Y and W1) Models.
Fan Selection System Selection Call Energize Display
a
Auto Off None None None
Auto Off Fan G
On Off None G
Auto Cool None O None
Auto Cool or Auto Cooling O, G, Y
and
Auto Heat None B None
Auto Heat or Auto Heating B, W1
and
Auto Heat or Auto Heating B, W1, W2
, , and Aux Ht
Auto Em Heat None B Em Ht
Auto Em Heat Stage 1 heating B, E
, and Em Ht
Auto Em Heat Stage 2 heating B, E, W2
, , Em Ht and Aux Ht
Auto Auto None
O or B
b
None
a
System selection is displayed.
b
Based on last piece of equipment called (cooling = O or heating = B)
and Installer Setup selection.
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