Lennox Prodigy M2 Application Manual page 98

Energence units feature four separate compressor and refrigeration circuits that can provide up to four stages of mechanical
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).
The discharge supply air temperature setpoint resides in the unit controller, has a factory default setting, and can be ad-
justed at start−up. The user can adjust the setpoint either locally or remotely with the L Connection Network Unit Controller
software or at the unit controller board. The user cannot adjust the setpoint through a third party control device or software
program.
19.1.9.4. 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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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.
19.1.9.5. Heating demand (general operation)
Upon receiving a heating demand from the third party unit 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 operation. The
unit controller receives discharge supply air temperature information directly from the supply duct temperature sensor lo-
cated in the supply duct system. Based on this information, the unit controller turns on or off mechanical heating stages to
maintain the discharge supply air temperature setpoint (110°F default). Adding heat stages increases heat capacity while
removing heat stages decreases heat capacity.
The heating discharge air temperature set point resides in the unit controller, has a factory default setting, and may be ad-
justed at start up. The user can adjust the setpoint either locally or remotely with the L Connection Network Unit Controller
software. The user cannot adjust the setpoint through a third party control device or software program.
19.1.9.6. Heating Operation (Electric)
Energence 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 maintain the discharge air temperature setpoint.
19.1.9.7. Morning Warm Up
Energence units have an intelligent and innovative morning warm up control scheme. As the VAV system shifts from unoc-
cupied to occupied, the unit controller automatically keeps the economizer shut for 60 minutes (default) or until the first
cooling demand. On cold days this prevents unconditioned fresh outdoor air from entering the building and helps to reduce
energy usage. Because most VAV systems perform morning warm up before occupants enter the building, the absence of
fresh outdoor air typically does not cause any problems.
Upon the first call for heating in this scenario, the unit controller instructs the unit to turn on the heating section and start
supply fan operation. Because the unit controller controls the heat staging and supply fan operation based on actual dis-
charge supply air temperature control and supply duct static pressure, the rooftop unit automatically selects the proper stag-
ing and supply fan speed to ensure optimal performance.
Typically in this scenario all zones are below the desired room temperature setpoint so the VAV boxes will be fully open. This
causes the supply duct static pressure to be low so the unit controller speeds up the fan to maintain the supply duct static
pressure setpoint. As the supply fan speeds up and increases the total supply air volume, the heating section turns on addi-
tional stages to maintain the correct discharge supply air temperature setpoint. In the event the unit controller receives a call
for cooling from the third party unit controller, the unit controller switches to cooling mode and opens the economizer. This
intelligent control scheme helps prevent potential problems caused by stuck VAV box dampers and supply duct static over
pressurization.
19.1.9.8. Outdoor Air CFM Control
The Outdoor Air CFM Control option allows variable air volume units to minimize the effect of supply fan speed changes and
maintain a constant outdoor air CFM level. A sensor located in the outdoor air section of the unit measures the outdoor air
velocity and relays the information to the unit controller. Based on the velocity information, the unit controller automatically
adjusts the economizer position, offsetting the supply fan speed changes and maintaining a constant outdoor air CFM level.
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19. Sequence of Operation