90
22.3.1.8.
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.
22.3.2.
Discharge Air Temperature Control (4-Heat / 4-Cool)
22.3.2.1.
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.
22.3.2.2.
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.
22.3.2.3.
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. The user can not adjust the set point through a a third-party control
device or software program.
The M3 unit controller receives discharge supply air temperature information directly from the temperature sensor,
located in the supply duct system. Based on this information, the M3 unit controller activates the different compressor
stages to maintain the discharge supply air temperature set point (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
mechanical cooling operation.
For stage one operation, the M3 unit controller activates the first compressor (25% of total unit capacity).
For stage two operation, the M3 unit controller activates the second compressor (50% unit capacity).
For stage three operation, the M3 unit controller activates the third compressor (75% total unit capacity).
For stage four operation, the M3 unit controller activates the fourth compressor (100% unit capacity).
22.3.2.4.
Cooling Demand With Economizer
If outdoor air is suitable for free cooling and the unit has an economizer, the M3 unit controller opens the economizer and
uses fresh air for stage one cooling.
For stage two operation, the M3 unit controller activates one compressor.
For stage three operation, the M3 unit controller activates a second compressor.
For stage four operation, the M3 unit controller activates the remaining compressors (number three and four).
The M3 unit controller has direct control over the rooftop unit staging and economizer operation.
