Lennox Prodigy 2.0 Application Manual page 78

During morning warm-up the M3 Unit Controller keeps the fresh air damper closed based on M3 Unit Controller
configuration settings. Set points for minimum and maximum damper position and carbon dioxide control reside in the M3
Unit Controller memory, have factory default settings, and may be adjusted at start up. The user can change these settings
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either locally or remotely through Lennox L Connection Network Unit Controller Software. The user will not have the ability
to adjust the settings through third-party software or control devices.
19.1.3.2. Demand Control Ventilation
Demand control ventilation is used in applications where the demand for fresh outdoor air fluctuates during the occupied
time period. Using a carbon dioxide sensor connected directly to the M3 Unit Controller, the unit can intelligently increase or
decrease the amount of fresh outdoor air by changing the outdoor air damper position. The M3 Unit Controller has two
operation modes available, set point or proportional, to control the outdoor air damper position.
19.1.3.3. Fresh Air Tempering
In applications with large outdoor air requirements, fresh air tempering is used to minimize temperature fluctuations in the
conditioned space. The M3 Unit Controller controls discharge air temperature by energizing heating or cooling in response
to the discharge air temperature. Fresh air tempering only occurs during occupied periods when the blower is running and
when there is no heating or cooling demand from the space. The user must configure the M3 Unit Controller to turn on the
fresh air tempering option (see Parameter 156 - FRESH AIR HEAT SP and 170 - FRESH AIR COOL SP).
Heating is energized when discharge air temperature falls below fresh air heating set point (Parameter 156, 40°F default)
and terminates when the discharge air temperature rises above the set point plus the heating dead-band (Parameter 157,
10°F default). Cooling is energized when discharge air temperature rises above fresh air cooling set point (Parameter 170,
90°F typical) and terminates when the discharge air temperature falls below the set point minus the cooling dead-band
(Parameter 171, 10°F default). Fresh air tempering will operate up to four stages of heating and cooling to maintain
discharge air temperature. Standard heating and cooling demands will override FAT heating and cooling demands. Also,
when Parameter 113 (EN RET AIR TMP LMT) is set to 1 (ENABLE), the return air temperature limits set in Parameter 114
(COOL RET AIR LIMIT) and 115 (HEAT RET AIR LIMIT) are enforced on FAT operation as well.
IMPORTANT
For fresh air tempering modes to operate properly, the RT6 discharge sensor must be relocated to the supply air duct.
19.1.3.4. Hot Gas Bypass
By selecting the hot gas bypass option which is only available on E Box only, the unit can operate in low airflow applications
down to 12.5% of nominal capacity. As the suction line pressure decreases and the potential for coil frosting increases, the
mechanical system bypasses hot refrigerant gas from the first stage compressor discharge line back to the suction line. The
hot gas increases the pressure of the suction line and reduces the compressor capacity. A de-superheater valve bypasses
refrigerant from the liquid line and mixes it with the hot gas before entering the suction line to maintain the set point suction
gas superheat entering the compressor.
19.1.3.5. Discharge Air Cooling Reset Operation
Discharge air cooling reset operation saves energy by gradually increasing the discharge air set point as outside air
temperature decreases. This operation also reduces the potential for over-cooling if the zoning system is misapplied, has an
abnormal condition, or has a dominant zone. The M3 Unit Controller has various advanced discharge air cooling reset
options which can be selected at start up and are based on either return air temperature, outside air temperature, or both
return and outdoor air temperature.
19.1.3.6. Discharge Air Heating Reset Operation
Discharge air heating reset operation saves energy by gradually decreasing the discharge air set point as outside air
temperature increases. This operation reduces the potential for overheating if the zoning system is misapplied, has an
abnormal condition, or has a dominant zone. The M3 Unit Controller has various advanced discharge air heating reset
options which can be selected at start up and are based on either return air temperature, outside air temperature or both
return and outdoor air temperature.
19.1.3.7. Damper Position Control of Exhaust Fan (Building Pressure)
Energence units can control building static pressure with either a standard or high static power exhaust fan. Each fan type is
available in either a 50% (one fan) or 100% (two fans) configuration. Standard static power exhaust fans use a propeller
while high static power exhaust fans use a centrifugal blower. All units featuring power exhaust fans must also have an
economizer.
Control of the fans can occur based on damper position or building differential static pressure transducers located outside
the building and in the return duct. Control of power exhaust fans can occur through the M3 Unit Controller, third-party device
or separate M3 Unit Controller.
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