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Delta T Diagnostics; Setting Up Alerts And Diagnostics - Honeywell Prestige 2.0 IAQ Installation Instructions Manual

Alerts and delta t diagnostics
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ALERTS AND DIAGNOSTICS
The Prestige thermostat uses alerts and diagnostics to
provide greater comfort and efficiency. Alerts and
diagnostics can notify customers when maintenance or
service is needed, and display your contact information to
make it easy for them to reach you.

Delta T Diagnostics

If discharge and return air sensors are installed, the
thermostat can track system performance over time. It
measures this as "Delta T." The thermostat monitors Delta
T and displays an alert on the home screen when the
system exceeds the limits you set.
Delta T Diagnostics tells you if the system is performing
above or below expected standards which would normally
go unnoticed, and may cause unnecessary energy use. It
can also detect and warn about problems early, before
heating or cooling equipment fails.
The thermostat will measure and record Delta T of the
system for each stage you test. This information can be
used to set the proper Delta T fault limits of the system.
When the system operates outside those limits multiple
times (see "Advanced Options for Delta T Diagnostics"
beginning on page 6), an alert is recorded in the log. If
configured to do so, the system will then display an alert
to the homeowner, along with your contact information.
Before You Set Up Delta T
Diagnostics
Refer to the information below for tips on installation and
setup of Delta T Diagnostics.
1. Refer to Fig. 1–5 for the placement of the Discharge
and Return Air Sensors.
2. In gas or oil forced air systems, Delta T will continue
to rise for several minutes even after Delta T begins
to stabilize. Be sure the Maximum Delta T Limit is
set higher than the expected stable Delta T. See
Fig. 7.
DELTA T BEGINS TO STABILIZE
DELTA T NOT STABLE
RUN TIME WHEN THERMOSTAT
COMPARES DELTA T TO THE
MINIMUM AND MAXIMUM DELTA T LIMITS
ALERTS AND DELTA T DIAGNOSTICS WITH THE PRESTIGE® 2.0 IAQ THERMOSTAT
MAXIMUM DELTA T LIMIT
MINIMIUM DELTA T LIMIT
DELTA T STABLE
RUN TIME
Fig. 7.
3. Delta T can be affected by indoor and outdoor
conditions for heat pumps and cooling systems.
Consider the total range of normal performance
when setting the Delta T Limits.
For example, in cooling, you might have a Delta T of
20 °F when the outdoor humidity is 50% and a
Delta T of 16 °F when the outdoor humidity is 85%.
You can either set Limits further apart and monitor
Delta T during all indoor and outdoor conditions or
set Limits closer together and turn off diagnostics
during certain indoor and outdoor conditions (see
"Advanced Options for Delta T Diagnostics"
beginning on page 6).
For example, you can set limits closer together and
then turn off diagnostics when outdoor temperature
is above 90 degrees and outdoor humidity is above
85%.
4. Verify the filter is clean and all the registers are
open before running an equipment test.
5. Select a Run Time when Delta T begins to stabilize
during the equipment test.
6. Set Minimum and Maximum Delta T Limits based
on what you consider to be unacceptable
performance from the heating and cooling
equipment.
NOTE: When the system operates below the
7. Delta T Diagnostics is only for non-zoned forced air
systems.
8. The thermostat does not provide Heat or Cool Delta
T Diagnostics when it is set to control an
Economizer module (ISU 2220).
9. The thermostat cannot be setup for Heat Delta T
Diagnostics when the thermostat is used with an
external fossil fuel kit (ISU 2190).

Setting up Alerts and Diagnostics

1. Set up the Return and Discharge Air Sensors by
selecting the check boxes on the screen. These
sensors are used to measure Delta T.
M31489
3
Minimum Limit or above the Maximum
Limit multiple times (Table 1), an alert is
recorded in the log. If configured to do so,
the thermostat will display an alert to the
user, along with your contact information.
Fig. 8.
69-2678EFS—03

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