Honeywell T7200D Product Data page 21

T7200D,E, T7300D,E,F AND Q7300 SERIES 2000 PROGRAMMABLE COMMERCIAL THERMOSTATS AND SUBBASES
(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
PROPORTIONAL COOL
CONTROL POINT
P+I CONTROL
POINT
PROPORTIONAL HEAT
CONTROL POINT
THERMOSTAT
HEAT SETPOINT
HEATING
100 50
PERCENT LOAD
thermostats. See Fig. 17.
Fig 17. Proportional temperature control
versus P+I temperature control.
Equipment Protection
As part of the operational sequence, the T7200/T7300
microprocessor also incorporates minimum on and off times
for all heating and cooling stages. Minimum on time is set in
the installer setup number 32. Using the minimum on and off
times assures that rapid cycling of equipment does not occur,
which extends equipment life. Minimum on and off times are
set in the Installer Setup.
T7200/T7300 Thermostat Operation
Startup
When power to the thermostat is turned on, a startup and
initialization program begins. The startup occurs only on initial
powerup. After total loss of power for an extended period, the
current time and day may need to be set, but the user
program is held. The initial default values are heating 68°F
(20°C) and cooling 78°F (26°C) for the Occupied periods.
Unoccupied default values are heating 55°F (13°C) and
cooling 90°F (32°C).
NOTE: The thermostat controls to the Unoccupied default
setpoints of 55°F (13°C) for heat and 90°F (32°C) for
cool when no program is set.
THERMOSTAT
COOL SETPOINT
P+I CONTROL POINT
COOLING
0 50 100
M4414
Occupied Operation
When the thermostat is operating in the Occupied period, the
temperature is controlled to the occupied heat or cool
setpoint. The normally open (A1 ) auxiliary relay contacts are
closed and the normally closed (A3) auxiliary relay contacts
are opened during the Occupied periods (if the subbase
being used has this option). The fan operates as follows: fan
selection can be set to On (always energized) or Auto (cycles
with Y1 or W1).
Unoccupied Operation
When the thermostat is operating in the Unoccupied period,
the temperature is controlled to the Unoccupied heat or cool
setpoint. The normally open (A1) relay contact is open and
the normally closed (A3) relay contact is closed. The fan
operates as follows: fan is always intermittent (cycles with Y1
or W1).
Intelligent Recovery® Feature
Intelligent Recovery® feature is a Honeywell trademark for
the way the thermostat controls the heating and cooling
equipment during recovery from Unoccupied to Occupied
setting. During recovery, the control point changes gradually
rather than jumping from the energy saving setting to the
comfort setting all at once.
When the Intelligent Recovery® feature is used in heating,
the control point raises gradually, maximizing the use of the
more economical first stage heat to bring the sensed
temperature to the desired comfort setpoint. This minimizes
using the typically more expensive second-stage heat.
The advantages are:
• Comfort setting is achieved at the programmed time and
maintained regardless of weather conditions; occupants
are comfortable.
• Drafts from low temperature discharge air are minimized
during occupied periods.
• Thermostat automatically uses the more economical first
stage of heat as the primary heat source during recovery,
avoiding the use of the expensive second stage heating.
• Comfort and energy savings can be achieved in both
heating and cooling.
• The thermostat reduces heat cycling, extending
equipment life.
Recovery from Unoccupied
The heating heat pump recovery ramp is 3°F (1.6°C) per
hour, which differs from the 5°F (2.8°C) per hour for
conventional systems. The 3°F helps the system use the
economical heat pump more and the expensive auxiliary heat
less. The cooling ramp is 5°F, the same as for conventional
systems.
Conventional System
The T7200 and T7300D,F Thermostats with Q7300A,G,H
Subbases are designed for conventional heat/cool applications.
Heat Pump Operation
The T7200E and T7300E,F Thermostats with Q7300C,D,H
Subbases are used for heat pump applications. Additional
information is required when configured for heat pump
applications.
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