®
T8600D, T8601D AND T8602D CHRONOTHERM IV DELUXE PROGRAMMABLE THERMOSTATS
THERMOSTAT
COOL SETPOINT
Using Daylight Savings Time Feature
This feature allows you to change in and out of Daylight
PROPORTIONAL COOL
Savings Time with a key press. When the Daylight Time Key is
pressed in the fall, the time will go back one hour. In the
spring, the time will go ahead one hour and the display will
show DST. See Setting the Current Day and Time section for
initial setting instructions.
CONTROL POINT
P+I CONTROL
POINT
P+I CONTROL POINT
NOTE: Pressing the Daylight Time Key more than once
within a five minute period will scroll you through
various time options (Example: one hour earlier or
later with or without DST). Pressing the Daylight
Time Key six times in a five minute period will return
you to your original settings.
PROPORTIONAL HEAT
CONTROL POINT
THERMOSTAT
HEAT SETPOINT
HEATING
COOLING
50
100
50
0
100
PERCENT LOAD
M4414
AM
Room
Time
Set Program
Leave
Return
Fig 13. Proportional temperature control versus P+I
temperature control.
Daylight
Time
ProR
g
u
r
n
am
S
De at yC / uT ri mr e en t
Wake
Sleep
Fan
Tue
Wake
System
Heat
Hold Temp
Day
H
S
eat tt /i Cn go so l
e
System
Fan
DaT
y
i ml ig
e
ht
Auto
Copy
M10341
Operation Sequence
Displaying the Outdoor Temperature
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.
If your thermostat is equipped with an outdoor sensor, you
can check the temperature at the sensor by pressing i
once.
Time
Set Program
Leave
Return
ProR
g
u
r
n
am
S
De at yC / uT ri mr e en t
Wake
Sleep
Fan
Outdoor
Hold Temp
Day
H
S
e
e
at tt /i Cn go so l
System
NOTE: Not all the thermostat models have all the terminals
listed in the Energize column.
DaT
y
i ml ig
e
ht
Copy
M10342
Table 10. Conventional System Sequence of Operation.
Selection
OPERATION
Fan
System
Call
None
None
Energize
None
Display
None
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.
Auto Off
On
Off
G
Auto Cool
None
O
None
Auto Cool or Auto
Cooling O, G and Y
and
Auto Heat
None
B
None
The thermostat microprocessor simultaneously gathers,
compares and computes data. Using this data, it controls a
wide variety of functions. The special proprietary algorithm
a
Auto Heat or Auto
Heating B and W
b
Auto Auto
a
None
O or B
None
(
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.
When electric heat fan is selected, G is energized and fan
symbol is displayed.
Based on last piece of equipment called (cooling = O or
heating = B) and Installer Setup selection.
b
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.
Equipment Protection
As part of the operational sequence, the thermostat
microprocessor also incorporates minimum off time for all
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.
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.
68-0164—1
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