Operation - Honeywell T8524 Deluxe Product Data

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 phenonemon that most people
in the industry know and accept. Many factors contribute to
offset including switch diffewrential, 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 that 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 the 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 in 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.
PROPORTIONAL COOL
CONTROL POINT
P+I CONTROL
POINT
PROPORTIONAL HEAT
CONTROL POINT
THERMOSTAT
HEAT SETPOINT
HEATING
100 50
PERCENT LOAD
Fig. 13. Proportional temperature
versus P+I temperature control.
THERMOSTAT
COOL SETPOINT
P+I CONTROL POINT
COOLING
0 50 100
M4414
T8524 DELUXE ELECTRONIC THERMOSTAT
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 7 for specific information.
Table 7. Multistage System Sequence of Operation.
System
Fan System
Auto Off None
On Off None
Auto Cool None
Auto Cool or Auto Stage 1
Cooling
Auto Cool or Auto Stage 2
Cooling
Auto Heat None
Auto Heat or Auto Stage 1
Heating
Auto Heat or Auto Stage 2
Heating
Auto Auto None
a
G is energized and fan symbol is displayed on dual fuel
models when set for electric heat.
b
Based on last piece of equipment called (cooling=O or
heating=B) and Installed Setup section.
11
Call Energize Display
None None
G
O None
O, G, Y1
and
O, G, Y1
and Y2
and
B None
a
B, G , and
W1
and
a
B, G , W1
and W2
and
b
None
O or B
68-0202