Honeywell T8611G Chronotherm IV Deluxe, Manual

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T8611G CHRONOTHERM ® IV DELUXE PROGRAMMABLE HEAT PUMP THERMOSTAT
68-0165—1 17
OPERATION
P+I Control
The thermostat microprocessor based control requires that
the user understands temperature control and thermostat
performance. A conventional electromechanical or electronic
thermostat does not control temperature precisely at setpoint.
Typically, there is an offset (droop) in the control point as the
system load changes. This is a phenomenon that most people
in the industry know and accept. Many factors contribute to
offset including switch differential, thermal lag, overshoot,
cycle rates and system load.
The thermostat microprocessor simultaneously gathers,
compares and computes data. Using this data, it controls a
wide variety of functions. The special proprietary algorithm
(program) in the thermostat eliminates the factors causing
offset. This makes temperature control more accurate than
the conventional electromechanical or electronic thermostats.
The temperature control algorithm is called proportional plus
integral (P+I) control.
The thermostat sensor, located on the thermostat or remote,
senses the current space temperature. The proportional error
is calculated by comparing the sensed temperature to the
programmed setpoint. The deviation from the setpoint is the
proportional error.
The thermostat also determines integral error, which is a
deviation based on the length of error time. The sum of the
two errors is the (P+I) error. The cycle rate used to reach and
maintain the setpoint temperature is computed using the P+I.
The addition of the integral error is what differentiates the
thermostat from many other electronic and electromechanical
thermostats. See Fig. 13.
Operation Sequence
The thermostat energizes specific terminals depending what
the Fan and System are set to. The LCD will display the time,
room temperature, system and fan selection. Symbols will be
displayed when the heating, cooling or fan is energized. See
Table 10 for specific information.
NOTE: Not all the thermostat models have all the terminals
listed in the Energize column.
Table 10. Heat Pump System Sequence of Operation.
Fig. 13. Proportional temperature control
versus P+I temperature control.
HEATING COOLING
PERCENT LOAD
TEMPERATURE
THERMOSTAT
HEAT SETPOINT
P+I CONTROL
POINT
PROPORTIONAL COOL
CONTROL POINT
THERMOSTAT
COOL SETPOINT
P+I CONTROL POINT
PROPORTIONAL HEAT
CONTROL POINT
M4414
100 50 0 50 100
Equipment Protection
As part of the operational sequence, the thermostat
microprocessor also incorporates minimum off time for all
heating and cooling stages. Using the minimum off time
assures that rapid cycling of equipment does not occur, which
extends equipment life. Minimum off times are set in the
Installer Setup.
Selection
Fan System Call Energize Display
Auto Off None None None
On Off None G
Auto Cool None O or O/B
a
None
Auto Cool or
Auto Stage 1
Cooling
O or O/B
a
with
G and Y1
and
Auto Heat None
B or O/B
a
None
Auto Heat or
Auto Stage 1
heating
B or O/B
a
with
W1 and G
and
Auto Heat or
Auto Stage 2
heating
B or O/B
a
with
W2, W1 or Y1
and G
, ,
and Aux Ht
Auto Em Heat None
B or O/B
a
with
X1
Em Ht
Auto Em Heat Stage 1
heating
B or O/B
a
with
X1 and E and G
(select models)
,
and Em Ht
Auto Em Heat Stage 2
heating
B or O/B
a
with
X1, E and W2
and G (select
models)
, ,
Em Ht and
Aux Ht
Auto Auto None
O/B
a
, O or B
b
None
a
Configure O/B (select models) in Installer Setup
number 29.
b
Based on last piece of equipment called (cooling = O or
heating = B) and Installer Setup selection.