Lennox Prodigy M2 Application Manual page 96

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For stage three operation, the unit controller activates a second compressor.
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For stage four operation, the unit controller activates the remaining compressors (number three and four).
The unit controller has direct control over the rooftop unit staging and economizer operation.
19.1.6.5. Heating Demand (General Operation)
Upon receiving a heating demand from a thermostat or a third party controller, the unit controller instructs the unit to maintain
a heating discharge air temperature setpoint. The unit controller has direct control over the rooftop unit heating staging op-
eration. The unit controller receives discharge supply air temperature information directly from the temperature sensor lo-
cated in the supply duct. Based on this information, the unit controller activates the different heating stages to maintain the
discharge supply air temperature setpoint (110°F default). Turning on additional heating stages increases the heating ca-
pacity, while turning off heating stages decreases the heating capacity. The heating discharge air temperature setpoint re-
sides in the unit controller, has a factory default setting, and may 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 third party control device or software program.
19.1.6.6. Heating Operation (Electric)
Units feature multiple electric heat sections available in sizes from 30 kW to 180 kW (depending on unit size and voltage).
Units can provide up to four stages of mechanical heating depending on the size of the electric heater. Staged operation
occurs similar to cooling operation, with the unit controller activating or deactivating sections of the electric heater to main-
tain the discharge air temperature setpoint.
19.1.7. Constant Air Volume (CAV) Units in Single Zone Applications with a Thermostat or Third Party
Unit Controller (2 Heat / 2 Cool)
19.1.7.1. Unit Controller Operation
When using a third−party unit controller and the unit controller is operating in the thermostat mode, a packaged rooftop unit
can provide up to two stages of mechanical heating and cooling operation. To operate correctly, a unit controller must pro-
vide the following wiring connections to the unit controller:
1. Ventilation demand
2. Occupied demand
3. Heating demand one
4. Heating demand two
5. Cooling demand one
6. Cooling demand two
In this configuration the third party unit controller will control the rooftop unit staging and general operation. The unit control-
ler functions primarily to determine unit error codes, provide diagnostic information and maintain safe operating limits.
19.1.7.2. Unit Sequence Of Operation
Constant air volume units in bypass zoning applications featuring a Lennox or third party unit controller with the unit control-
ler operating in thermostat mode, have the same basic heating and cooling unit sequence of operations as constant air
volume units in single zone applications featuring a third party unit controller, with the unit controller operating in thermostat
mode. For specific information, refer to the Constant Air Volume in Single Zone Applications with a Thermostat or Third
Party Unit Controller section.
The following sequence of operation information is specific to constant air volume units in bypass zoning applications.
19.1.7.3. Supply Duct Bypass Damper
To maintain accurate supply duct static pressure control, constant volume units in bypass zoning applications use a bypass
damper between the supply and return air ducts. In this scenario, the supply duct static pressure transducer and damper
connect directly to the third party unit controller. Based on actual static pressure relative to setpoint, the third party unit con-
troller either modulates open or closes the damper. It the damper modulates further closed, the static pressure in the supply
air duct increases. If the damper modulates further open, the static pressure in the supply air duct decreases. The unit con-
troller does not have direct control over the bypass damper in this scenario.
19.1.8. Constant Air Volume Units in Bypass (CAVB) Zoning Applications with a Third Party Unit Con-
troller and the Unit Operating in Discharge Air Temperature Control (4 Heat / 4 Cool)
19.1.8.1. Unit Controller Operation
When using a third party unit controller and the unit controller is operating in thermostat mode and 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 third party unit controller must provide the following wiring connections to the unit controller:
1. Ventilation demand
2. Occupied demand
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19. Sequence of Operation