Calibration - Lennox Prodigy 2.0 Application Manual

18. Advanced Airflow System (Smart Airflow
units)
The optional factory installed Advanced Airflow System employs a pressure sensor equipped economizer and an ECM
blower motor. This feature enables the Prodigy M3 Unit Controller to accurately measure and control the Supply Airflow and
Outdoor Airflow.

18.1. Calibration

Calibration is a procedure which determines the relationship between motor torque and supply airflow by collecting
operational data from the system once it has been applied in the field and the appropriate filters are installed. The goal is to
discover appropriate PWM settings which to drive the ECM blower motor and that correspond to various Supply Airflow
targets.
Once installed, each unit will undergo a calibration process. Calibration starts automatically with the first blower demand
received after 24 hours completion of the installation. Installer can also trigger the calibration manually through the Display
Menu option. Calibration is a onetime process after the installation and once successful, calibration data will be retained in
M3 Unit Controller until the calibration is re­triggered manually.
User can change the supply airflow settings without re­triggering the calibration any time. If any of the new airflow targets are
set to a value less than the minimum supply airflow as stored in calibration table then Alarm Code 140 (Advance Airflow CFM
Unattainable Target Too Low) is triggered. If any of the supply airflow targets is set to a value greater than the maximum
supply airflow as stored in the calibration table then Alarm Code141 (Advance Airflow CFM Unattainable Target Too High) is
triggered.
The below steps are sequentially carried out during the calibration process.
1. Initialization : All components in roof top units except for the blower are turned OFF. System will wait for outdoor air
damper to close. Then the blower is run at minimum PWM setting of 20%.
2. Blower Diagnostics: PWM is gradually increased in steps from 20% to 100%, with a torque value set by Parameter
247 (Advance Airflow Blower Ramp Rate Set Point). At each step PWM, RPM and calculated Supply Airflow are
recorded internally to a calibration table. In applications where the supply static pressure is high, blower calibration will
stop once blower RPM has crossed the cutoff range (1250 rpm – for ECM motors) even before reaching 100% PWM.
In applications where the Supply Static is less, blower calibration will stop once the calculated supply airflow is greater
than the RTU airflow specification of 480 CFM/ton. If the calculated Supply Static Pressure is greater than 1.8" or less
than ­0.1" Calibration process would be failed.
3. Damper Diagnostic: PWM is set to a value to generate 400 CFM/ton Supply Airflow and then damper is moved to 0%,
50% and 100% and the corresponding differential pressure is recorded and diagnosed. If the maximum airflow found
in Blower calibration is less than 400 CFM/ton then PWM corresponding to maximum Airflow is used.
18.2. Supply Airflow Measurement and Control
Based on the blower demand (Heating, Cooling, Ventilation and Smoke) the corresponding Parameters 12, 13, 14, 17 and
18 are chosen as target airflows. Using the linear interpolation method the corresponding % PWM for the target airflow is
calculated from the calibration table. Blower is run at this percentage PWM and the actual airflow is measured periodically
and compared with the target.
If the RPM feedback of the blower is less than 50 rpm then Alarm 135 (Advance Airflow No Supply Airflow) is triggered.
If the actual airflow is lesser than the target percentage set by Parameter 234 - Advance Airflow Low Speed CFM Alarm Set
Point (default 25%) for more than the time duration set by Parameter 235 - Advance Airflow Low Speed CFM Alarm
Evaluation (default 1800 seconds), then an Alarm Code 134 (Low Supply Airflow) is triggered. The alarm code is cleared
only if the above stated condition is not present persistently for twice the time set by Parameter 235 during an active blower
demand.
™
) in High Efficiency A Box (3-5 Ton
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