Operation; Adaptive Intelligent Recovery™ Operation; What To Expect During Recovery From Energy Savings In Heating; Thermal Performance With T8621 - Honeywell CHRONOTHERM T8621A User Manual

T8621A,C,D

OPERATION

ADAPTIVE INTELLIGENT RECOVERY™

OPERATION

Adaptive Intelligent Recovery™ is the Honeywell trade-
mark for the way the T8621 controls the heating and
cooling equipment during recovery from an energy sav-
ings setting to a comfort setting. During recovery, the
control point changes gradually rather than jumping from
the energy savings setting to the comfort setting all at once.
This provides additional energy savings.
In both heating and cooling, the thermostat monitors
recovery each day and adjusts the next day recovery start
time. This ensures that the building is at the desired
temperature at the programmed time, regardless of the
outdoor temperature. Recovery time varies depending on
the weather conditions and the building heating/cooling
system.
The advantages are:
• Comfort setting is achieved at the programmed time
and maintained regardless of weather conditions;
occupants come home and wake up to comfort.
• Drafts from low temperature discharge air are mini-
mized during occupied periods.
• Comfort and energy savings can be achieved in both
heating and cooling.
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
thermostat.
WHAT TO EXPECT DURING RECOVERY
FROM ENERGY SAVINGS IN HEATING
The T8621 controls the heating equipment based on the
indoor sensed temperature, which is a combination of air
temperature and wall temperature.

THERMAL PERFORMANCE WITH T8621

During severe weather, the T8621 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 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 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
T8621 maintains space temperature within one degree of
setpoint, when the temperature has stabilized after an
energy savings period.
This zero droop performance of the T8621 provides
improved occupant comfort and energy savings. Occu-
pants do not need to continually adjust thermostat settings
to maintain desired temperature, even during severe
weather.

MINIMUM-OFF TIMING

A minimum-off timer in the T8621 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, and when the system switch is
moved. If the compress or 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 only cooling.
28
Operation