Honeywell VisionPRO IAQ Product Data page 32

®
VISIONPRO IAQ TOTAL HOME COMFORT SYSTEM
NOTE: It takes about a week for the thermostat to adjust to
local weather, the schedule, the construction of the
home and the heating and/or cooling system. Each
day it adjusts the next day's recovery start time
accordingly.
P+I Control
The thermostat microprocessor-based control requires that the
user understands temperature control and thermostat
performance. A conventional mechanical 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 mechanical 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 mechanical
thermostats. See Fig. 33.
PROPORTIONAL COOL
CONTROL POINT
P+I CONTROL
POINT
PROPORTIONAL HEAT
CONTROL POINT
THERMOSTAT
HEAT SETPOINT
HEATING
100 50
PERCENT LOAD
Fig. 33. Proportional temperature control versus P+ I
temperature control.
68-0287—1
THERMOSTAT
COOL SETPOINT
P+I CONTROL POINT
COOLING
0 50 100
M4414
Minimum Off-Timer
The Thermostat has built-in compressor protection (minimum-
off timer) that prevents the compressor from restarting too
early after a shutdown. The minimum-off timer is activated after
the compressor turns off.
If there is a call during the minimum-off timer, the thermostat
shows "Wait" in the display.
FAN
Inside
AUTO
SYSTEM
HEAT
COOL
SCHED
When the minimum-off timer expires, "Cool On" or "Heat On"
appears in the display and the compressor and fan turn on.
_________
a
Heat Pumps only.
Inside Humidity Level
The humidity level in the home is shown in the lower right
corner of the Home Screen.
NOTE: If an outdoor temperature sensor is present, the out-
door temperature will be displayed in this location
rather than the indoor humidity. To see indoor humid-
ity, display the humidity settings menu.
TUE
FAN
Inside
AUTO
SYSTEM
COOL
SCHED
If thermostat is set to Auto Changeover System mode, press
the More key until the humidity level is shown on the screen.
32
WED
Set To
Wait
Following
Schedule
AM
PM
Humidity
HOLD CLOCK SCREEN MORE
M23513
Set
Following
Schedule
PM
Humidity
HOLD CLOCK SCREEN MORE
M23678
a