Compressor Protection; P + I Control; Heat Differential - Honeywell Home T10 Product Data

Adaptive Intelligent Recovery® calculates the recovery ramp
based on how far the room temperature is away from the
temperature setting, previous equipment performance and
weather history, allowing the thermostat to start recovery at
the optimal time so it can reach the programmed temperature
setting at the programmed time. The T10 or T10+ thermostat
uses two recovery ramps when setup to control a heat pump
system. One ramp for the compressor and one ramp for the
auxiliary heat. Once the room temperature intersects the
compressor ramp, the compressor turns on until the setpoint
is reached. If the room temperature does not rise quickly
enough and intersects the second ramp, the auxiliary heat
turns on. It takes about one week for the thermostat to adjust
to weather conditions, equipment performance and
construction of the home. If the temperature setting is reached
too early or too late, the ramp is adjusted for the next day's
recovery. See Fig. 98.
Fig. 98.

Compressor Protection

The thermostat keeps the compressor off for a few minutes
before restarting, to prevent equipment damage. During this
"off" time, the message "Wait" is displayed on screen.

P + I Control

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.
Many factors contribute to offset including the switch
differential, thermal lag, overshoot, cycle rates and system
load.
The T10 or T10+ thermostat however, works much differently
than a conventional mechanical or electronic Thermostat
when droop is set to comfort. Droop is always set to comfort
and not adjustable when controlling a 2 stage furnace or 2
stage heat pump without aux heat. The proprietary algorithm
in the thermostat eliminates the factors causing offset (droop).
This makes temperature control more accurate than the
conventional mechanical or electronic thermostat. The
temperature control algorithm is called proportional plus
integral (P + I) control.
The thermostat sensor or indoor sensor senses the current
space temperature. The proportional error is calculated by
comparing the sensed temperature to the setpoint
temperature. The deviation from the setpoint is the
proportional error.
33-00462—05
COMPRESSOR SETPOINT
AUXILIARY HEAT SETPOINT
ROOM TEMPERATURE
WAKE
M6406C
The thermostat also determines integral error, which is a
deviation based on the length of error time (how long the
sensed room temperature has been away from the setpoint
temperature). 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 control algorithm.
The addition of the integral error is what differentiates the
thermostat from many other mechanical and electronic
thermostats.

Heat Differential

For stage 2 of conventional systems or 2
stage heatpump without aux heat
The thermostat will use the stage of heating as needed to
keep the indoor temperature within 1 °F (0.5 °C) degree of the
setpoint. The thermostat turns on stage 2 when the capacity
on stage 1 reaches 90%.
Heat pumps with electric aux heat when
droop is set to "comfort"
The thermostat will use the stage of heating as needed to
keep the indoor temperature within 1 °F (0.5 °C) degree of the
setpoint. The thermostat turns on Aux heat when the capacity
on highest compressor stage has reaches 90%.
Heat pumps with electric aux heat when
droop is set to 2°F or higher
(2 °F to 15 °F adjustable)
If the indoor temperature drops to the droop amount while the
highest compressor stage is running the thermostat will
continue to run the heatpump stages and also energize the
Aux heat.
For example, if the Backup Heat Droop is set to 2 °F (1.0 °C),
the indoor temperature must drop 2 °F (1.0 °C) below the
setpoint while the previous stage is running before the backup
heat turns on. Raising setpoint manually or by a schedule
change does not cause droop to run the backup heat. When
droop is set to other than comfort, the upstage timer setting is
also available.
Dual fuel Heat pumps with gas or oil
backup heat
If thermostat is configured to control dual fuel, the droop
cannot be set to comfort. It will default to 2 °F and can be
adjusted from 2 °F to 15 °F.
If the indoor temperature drops to the droop amount while the
highest compressor stage is running the thermostat will end
the call for the heatpump stages and run the fossil fuel heat
stage.
For example, if the Backup Heat Droop is set to 2 °F (1.0 °C),
the indoor temperature must drop 2 °F (1.0 °C) below the
setpoint while highest heatpump stage is running before the
thermostat will shut down the heat pump and run the fossil
fuel heat.
Raising setpoint manually or by a schedule change does not
cause droop to run the backup heat. When droop is set to
other than comfort, the upstage timer setting is also available.
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