Lennox Prodigy 2.0 Application Manual page 82

19.1.5.7. Humiditrol Dehumidification Operation - Dehumidification Demand
Upon a dehumidification demand, the M3 Unit Controller activates compressor number one (compressor two if applicable).
At the same time, the M3 Unit Controller activates solenoid valves to divert hot gas from compressor one (and compressor 2
if applicable) to the reheat coil. The cooled and dehumidifed air from the evaporator is then reheated as it passes through the
reheat coil. The de-superheated and partially condensed refrigerant continues to the outdoor condenser coil where
condensing is completed. The reheat coil is sized to offset most of the first and second stages (if applicable) of sensible
cooling effect during reheat only operation. This reduction in sensible cooling capacity extends compressor run time to
control humidity when cooling loads are light.
The unit will continue to operate in this mode until the dehumidification demand is satisfied. A heating demand will terminate
reheat operation.
The M3 Unit Controller relative humidity set point is factory configured for 60% and can be adjusted at the M3 Unit Controller
or with the L Connection Network Unit Controller software. For Network Control Panel (Network Control Panel) applications,
the humidity set point can be adjusted at the Network Control Panel. The M3 Unit Controller also has an option for an
external digital input to signal the dehumidification demand. This demand must be provided from an external third-party
DDC.
For unit model specific details, refer to the unit installation instruction.
19.1.5.8. Humiditrol Dehumidification Operation - Cooling Demand Only
The unit operates conventionally whenever there is a demand for cooling and no dehumidification demand. The unit can
provide up to two stages of mechanical cooling in this scenario. Free cooling is only permitted when an economizer is
present, there is no demand for dehumidification and outdoor air is suitable for this function.
19.1.5.9. Humiditrol Dehumidification Operation - Cooling and Dehumidification Demand
Stage one cooling demand with dehumidification demand: If both a dehumidification demand and a first stage cooling
demand occur, the system activates all applicable compressors plus the first-stage of reheat. This provides 100% humidity
removal capacity with approximately 50% cooling capacity.
Stage two cooling demand with dehumidification demand: A demand for second-stage cooling activates all compressors
plus terminates any reheat operation. This provides 100% humidity removal capability and 100% cooling capacity. The M3
Unit Controller activates all compressors until the cooling demand is satisfied.
19.1.6. Constant Air Volume Units in Single-Zone Applications with a Wired Thermostat or Third-Party
Unit Controller and the Unit Operating in Discharge Air Temperature Control (4-Heat / 4-Cool)
19.1.6.1. Unit Controller Operation
When using a thermostat or third-party controller with the M3 Unit Controller operating in the thermostat mode configured for
discharge air temperature control, a packaged rooftop unit can provide up to four stages of mechanical heating and cooling
operation.
To operate correctly, a thermostat or third-party controller must provide the following wiring connections to the M3 Unit
Controller:
1. Ventilation demand
2. Occupied demand
3. Heating demand
4. Cooling demand
In this configuration the M3 Unit Controller will control the rooftop staging and general operation. The thermostat or
third-party controller only informs the M3 Unit Controller if there is a specific demand. For example, if the thermostat or
third-party controller passes along a demand for cooling, the controller increases or decreases cooling stages to maintain
the discharge supply air temperature set point. Along with providing control of the rooftop unit, the M3 Unit Controller also
provides error codes, diagnostic information and maintains safe operating limits.
19.1.6.2. Ventilation Demand
Upon receiving a ventilation demand from the thermostat or M3 Unit Controller, the M3 Unit Controller activates the supply
fan. The supply fan operates at 100% capacity until the ventilation demand has been removed.
19.1.6.3. Cooling Demand
Upon receiving a cooling demand from the the thermostat or M3 Unit Controller, the M3 Unit Controller instructs the unit to
maintain a cooling discharge air temperature set point. The M3 Unit Controller has direct control over the rooftop unit
staging. The discharge supply air temperature set point resides in the M3 Unit Controller, has a factory default setting, and
can be adjusted at start-up. The user can adjust the set point either locally or remotely with Lennox' L Connection Network
Unit Controller software or at the M3 Unit Controller board. The user can not adjust the set point through a a third-party
control device or software program.
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