Honeywell T8611M

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 within +/-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