Lennox Prodigy M2 Application Manual page 95

The unit controller relative humidity setpoint is factory configured for 60% and can be adjusted at the unit controller or with
the L Connection Network Unit Controller software. For Network Control Panel (NCP) applications, the humidity setpoint
can be adjusted at the NCP. The 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.
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 pres-
ent, 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 de-
mand occur, the system activates all four 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 four compres-
sors plus terminates any reheat operation. This provides 100% humidity removal capability and 100% cooling capacity. The
unit controller activates all compressors until the cooling demand is satisfied
19.1.6. Constant Air Volume (CAV) Units in Single Zone Applications with a 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 unit controller with the 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 unit controller:
1. Ventilation demand
2. Occupied demand
3. Heating demand
4. Cooling demand
In this configuration the unit controller will control the rooftop staging and general operation. The thermostat or third party
unit controller only informs the unit controller if there is a specific demand. For example, if the thermostat or third party unit
controller passes along a demand for cooling, the controller increases or decreases cooling stages to maintain the discharge
supply air temperature setpoint. Along with providing control of the rooftop unit, the 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 unit controller, the 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 unit controller, the unit controller instructs the unit to maintain a
cooling discharge air temperature setpoint. The unit controller has direct control over the rooftop unit staging. The discharge
supply air temperature setpoint resides in the unit controller, has a factory default setting, and can be adjusted at start−up.
The user can adjust the setpoint either locally or remotely with Lennox' L Connection Network Unit Controller software or at
the unit controller board. The user can not adjust the setpoint through a a third party control device or software program.
The unit controller receives discharge supply air temperature information directly from the temperature sensor, located in
the supply duct system. Based on this information, the unit controller activates the different compressor stages to maintain
the discharge supply air temperature setpoint (55°F default). Increasing compressor stages provides more cooling capacity
while decreasing compressor stages provides less cooling capacity.
Energence units feature four separate compressors and refrigeration circuits that can provide up to four stages of mechani-
cal cooling operation.
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For stage one operation, the unit controller activates the first compressor (25% of total unit capacity).
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For stage two operation, the unit controller activates the second compressor (50% unit capacity).
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For stage three operation, the unit controller activates the third compressor (75% total unit capacity).
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For stage four operation, the unit controller activates the fourth compressor (100% unit capacity).
19.1.6.4. Cooling Demand With Economizer
If outdoor air is suitable for free cooling and the unit has an economizer, the unit controller opens the economizer and uses
fresh air for stage one cooling.
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For stage two operation, the unit controller activates one compressor.
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19. Sequence of Operation
PRODIGYT M2 UNIT CONTROLLER