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the auxiliary heat even when the T8611 is calling for it.
(Balance point is the outdoor temperature below which the
heat pump must call on auxiliary heat to help handle the
load.) The resulting unnecessarily long recovery times
reduce building energy savings.
When Adaptive Intelligent Recovery™ Is Used
Adaptive Intelligent Recovery™ is used during recov-
ery from energy savings. It is bypassed when the setpoint
is changed, and when the CHANGE TO LAST PERIOD,
SKIP NEXT PERIOD or HOLD TEMP key is pressed. If
Adaptive Intelligent Recovery™ is bypassed, the system
operates the stages of equipment like a conventional ther-
mostat.
WHAT TO EXPECT DURING RECOVERY
FROM ENERGY SAVINGS IN HEATING
The T8611 controls the heating equipment based on the
indoor sensed temperature, which is a combination of air
temperature and wall temperature.
In Mild Weather
When the outdoor temperature is mild, say 50
°
F [10
°
C], the recovery from energy savings will be handled
completely by the heat pump, without using the more
costly auxiliary heat. The heat pump starts only after the
control point has risen above the sensed temperature and
is locked on until the comfort setpoint is reached. During
the comfort period, the heat pump will cycle on and off as
needed to maintain the sensed temperature /-1
°
F
of the setpoint. During energy savings periods, the T8611
will call the heat pump on only if the sensed temperature
falls below the control point.
In Moderate Weather
When outdoor temperature is below the balance point
of the heat pump, the heat pump will run continuously
during the recovery period and the auxiliary heat will cycle
as necessary. During the comfort period, the heat pump
runs continuously and auxiliary heat cycles until the next
energy savings period begins. During energy savings, the
heat pump cycles on only when the sensed temperature
falls below the control point. Under these conditions,
auxiliary heat is typically not needed during the energy
savings period.
In Severe Weather
When the outdoor temperature is severe, say 0
°
F [-18
°
C], the heat pump is on continuously and auxiliary heat
cycles even during the energy savings period. When re-
covery from energy savings begins, the heat pump will
stay on and auxiliary heat will cycle. During recovery, the
auxiliary heat ON times will be long, and the OFF times
will be short. The ON times will shorten as the control
point approaches the comfort setpoint. During the comfort
period, the heat pump is on continuously and auxiliary heat
cycles until the next energy savings period. When energy
saving begins, the heat pump cycles off until the sensed
temperature falls below the control point. Although the
heat pump comes on when the sensed temperature falls
below the control point, the sensed temperature may lag 2
°
or 3
°
F below the control point because of the time required
to warm up the walls and furniture. Auxiliary heat will
cycle as necessary during the energy savings period.
THERMAL PERFORMANCE WITH T8611
During severe weather, the T8611 actually controls
closer to the setpoint than a conventional thermostat. This
is because the heat anticipator is replaced by two elec-
tronic control strategies—cycling by heat anticipation and
proportional plus integral control.
Electronic cycling by heat anticipation acts like a tradi-
tional heat anticipator, except that never needs adjustment
for various control circuit load currents. It cycles the heat
pump off slightly before the room temperature reaches the
setpoint to keep heat remaining in the ductwork from
overheating the room.
In severe weather, a conventional thermostat with a
heat anticipator tends to turn off the thermostat too soon,
so the effective control point is somewhat below the
setpoint. In very cold weather, the difference between
setpoint and effective control point may be 5
°
or 6
°
F [2
°
or 3
°
C] with a conventional thermostat. 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
T8611 controls space temperature within one degree of
setpoint, when the temperature has stabilized after an
energy savings period.
This zero droop performance of the T8611 provides
improved occupant comfort and energy savings. Occu-
pants do not need to continually adjust thermostat setting
to maintain desired temperature, even during severe
weather.
MINIMUM-OFF TIMING
A minimum-off timer in the T8611 ensures that the
compressor will not come on again for at least five minutes
after it turns off. The minimum-off timer is triggered when
the compressor goes off, or when the system switch is
moved. If the compressor turns off when the setpoint is
changed or the CHANGE TO LAST PERIOD key is
pressed, then the minimum-off timer is triggered. The
minimum-off timer operates during the first stage of both
heating and cooling.
T8611M
OPERATION
